// get user object from the storage
var user = await userManager.FindByIdAsync(userId);

// change username and email
user.Username = "NewUsername";
user.Email = "New@email.com";

// Persiste the changes
await userManager.UpdateAsync(user);

// generage email confirmation code
var emailConfirmationCode = await userManager.GenerateEmailConfirmationTokenAsync(user.Id);

// generate url for page where you can confirm the email
var callbackurl= "http://example.com/ConfirmEmail";

// append userId and confirmation code as parameters to the url
callbackurl += String.Format("?userId={0}&code={1}", user.Id, HttpUtility.UrlEncode(emailConfirmationCode));

var htmlContent = String.Format(
        @"Thank you for updating your email. Please confirm the email by clicking this link:
        <br><a href='{0}'>Confirm new email</a>",
        callbackurl);

// send email to the user with the confirmation link
await userManager.SendEmailAsync(user.Id, subject: "Email confirmation", body: htmlContent);



// then this is the action to confirm the email on the user
// link in the email should be pointing here
public async Task<ActionResult> ConfirmEmail(string userId, string code)
{
    var confirmResult = await userManager.ConfirmEmailAsync(userId, code);

    return RedirectToAction("Index");
}

public class ApplicationUser : IdentityUser
{
    public async Task<ClaimsIdentity> GenerateUserIdentityAsync(UserManager<ApplicationUser> manager)
    {
        // Note the authenticationType must match the one defined in CookieAuthenticationOptions.AuthenticationType
        var userIdentity = await manager.CreateIdentityAsync(this, DefaultAuthenticationTypes.ApplicationCookie);
        // Add custom user claims here
        return userIdentity;
    }

    [MaxLength(256)]
    public string UnConfirmedEmail { get; set; }//this is what we add

}

//
    // POST: /Account/Login
    [HttpPost]
    [AllowAnonymous]
    [ValidateAntiForgeryToken]
    public async Task<ActionResult> Login(LoginViewModel model, string returnUrl)
    {
        if (!ModelState.IsValid)
        {
            return View(model);
        }

        var allowPassOnEmailVerfication = false;
        var user = await UserManager.FindByEmailAsync(model.Email);
        if (user != null)
        {
            if (!string.IsNullOrWhiteSpace(user.UnConfirmedEmail))
            {
                allowPassOnEmailVerfication = true;
            }
        }


        // This now counts login failures towards account lockout
        // To enable password failures to trigger account lockout, I changed to shouldLockout: true
        var result = await SignInManager.PasswordSignInAsync(model.Email, model.Password, model.RememberMe, shouldLockout: true);
        switch (result)
        {
            case SignInStatus.Success:
                return RedirectToLocal(returnUrl);
            case SignInStatus.LockedOut:
                return View("Lockout");
            case SignInStatus.RequiresVerification:
                return allowPassOnEmailVerfication ? RedirectToLocal(returnUrl) : RedirectToAction("SendCode", new { ReturnUrl = returnUrl, RememberMe = model.RememberMe });
            case SignInStatus.Failure:
            default:
                ModelState.AddModelError("", "Invalid login attempt.");
                return View(model);
        }
    }

public class IndexViewModel
{
    public bool HasPassword { get; set; }
    public IList<UserLoginInfo> Logins { get; set; }
    public string PhoneNumber { get; set; }
    public bool TwoFactor { get; set; }
    public bool BrowserRemembered { get; set; }

    public string ConfirmedEmail { get; set; } //add this
    public string UnConfirmedEmail { get; set; } //and this
}

var userId = User.Identity.GetUserId();
        var currentUser = await UserManager.FindByIdAsync(userId);

        var unConfirmedEmail = "";
        if (!String.IsNullOrWhiteSpace(currentUser.UnConfirmedEmail))
        {
            unConfirmedEmail = currentUser.UnConfirmedEmail;
        }
        var model = new IndexViewModel
        {
            HasPassword = HasPassword(),
            PhoneNumber = await UserManager.GetPhoneNumberAsync(userId),
            TwoFactor = await UserManager.GetTwoFactorEnabledAsync(userId),
            Logins = await UserManager.GetLoginsAsync(userId),
            BrowserRemembered = await AuthenticationManager.TwoFactorBrowserRememberedAsync(userId),
            ConfirmedEmail = currentUser.Email,
            UnConfirmedEmail = unConfirmedEmail
        };

<dt>Email:</dt>
    <dd>
        @Model.ConfirmedEmail
        @if (!String.IsNullOrWhiteSpace(Model.UnConfirmedEmail))
        {
            <em> - Unconfirmed: @Model.UnConfirmedEmail </em> @Html.ActionLink("Cancel", "CancelUnconfirmedEmail",new {email=Model.ConfirmedEmail})
        }
        else
        {
            @Html.ActionLink("Change Email", "ChangeEmail")
        }
    </dd>

public class ChangeEmailViewModel
{
    public string ConfirmedEmail { get; set; }
    [Required]
    [EmailAddress]
    [Display(Name = "Email")]
    [DataType(DataType.EmailAddress)]
    public string UnConfirmedEmail { get; set; }
}

public ActionResult ChangeEmail()
    {
        var user = UserManager.FindById(User.Identity.GetUserId());
        var model = new ChangeEmailViewModel()
        {
            ConfirmedEmail = user.Email
        };

        return View(model);
    }

@model ProjectName.Models.ChangeEmailViewModel
@{
ViewBag.Title = "Change Email";
}

<h2>@ViewBag.Title.</h2>

@using (Html.BeginForm("ChangeEmail", "Account", FormMethod.Post, new { @class = "form-horizontal", role = "form" }))
{
    @Html.AntiForgeryToken()
    <h4>New Email Address:</h4>
    <hr />
    @Html.ValidationSummary("", new { @class = "text-danger" })
    @Html.HiddenFor(m=>m.ConfirmedEmail)
    <div class="form-group">
        @Html.LabelFor(m => m.UnConfirmedEmail, new { @class = "col-md-2 control-label" })
        <div class="col-md-10">
            @Html.TextBoxFor(m => m.UnConfirmedEmail, new { @class = "form-control" })
        </div>
    </div>
    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" class="btn btn-default" value="Email Link" />
        </div>
    </div>
}

[HttpPost]
    public async Task<ActionResult> ChangeEmail(ChangeEmailViewModel model)
    {
        if (!ModelState.IsValid)
        {
            return RedirectToAction("ChangeEmail", "Manage");
        }

        var user = await UserManager.FindByEmailAsync(model.ConfirmedEmail);
        var userId = user.Id;
        if (user != null)
        {
            //doing a quick swap so we can send the appropriate confirmation email
            user.UnConfirmedEmail = user.Email;
            user.Email = model.UnConfirmedEmail;
            user.EmailConfirmed = false;
            var result = await UserManager.UpdateAsync(user);

            if (result.Succeeded)
            {

                string callbackUrl =
                await SendEmailConfirmationTokenAsync(userId, "Confirm your new email");

                var tempUnconfirmed = user.Email;
                user.Email = user.UnConfirmedEmail;
                user.UnConfirmedEmail = tempUnconfirmed;
                result = await UserManager.UpdateAsync(user);

                callbackUrl = await SendEmailConfirmationWarningAsync(userId, "You email has been updated to: "+user.UnConfirmedEmail);


            }
        }
        return RedirectToAction("Index","Manage");
    }

private async Task<string> SendEmailConfirmationWarningAsync(string userID, string subject)
    {
        string code = await UserManager.GenerateEmailConfirmationTokenAsync(userID);
        var callbackUrl = Url.Action("ConfirmEmail", "Account",
           new { userId = userID, code = code }, protocol: Request.Url.Scheme);
        await UserManager.SendEmailAsync(userID, subject,
           "Please confirm your account by clicking <a href="" + callbackUrl + "">here</a>");

        return callbackUrl;
    }

public async Task<ActionResult> CancelUnconfirmedEmail(string emailOrUserId)
    {
        var user = await UserManager.FindByEmailAsync(emailOrUserId);
        if (user == null)
        {
            user = await UserManager.FindByIdAsync(emailOrUserId);
            if (user != null)
            {
                user.UnConfirmedEmail = "";
                user.EmailConfirmed = true;
                var result = await UserManager.UpdateAsync(user);
            }
        }
        else
        {
            user.UnConfirmedEmail = "";
            user.EmailConfirmed = true;
            var result = await UserManager.UpdateAsync(user);
        }
        return RedirectToAction("Index", "Manage");

    }

var result = UserManager.ConfirmEmail(userId, code);
 if (result.Succeeded)
 {

     var user = UserManager.FindById(userId);
     if (!string.IsNullOrWhiteSpace(user.UnConfirmedEmail))
     {
         user.Email = user.UnConfirmedEmail;
         user.UserName = user.UnConfirmedEmail;
         user.UnConfirmedEmail = "";

         UserManager.Update(user);
     }
 }