asp.net membership change password without knowing old one
membershipUser.ChangePassword(userWrapper.OldPassword, userWrapper.Password)

string username = "username";
 string password = "newpassword";
 MembershipUser mu = Membership.GetUser(username);
 mu.ChangePassword(mu.ResetPassword(), password);

string randompassword = membershipUser.ResetPassword();
membershipUser.ChangePassword(randompassword , userWrapper.Password)

membershipUser.ChangePassword(membershipUser.ResetPassword(), userWrapper.Password)

MembershipUser user;
 user = Membership.GetUser(userName,false);
 user.ChangePassword(user.ResetPassword(),"123456");