c sharp update login whatever

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Button3.Enabled = false;
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(@"Data Source=(LocalDB)\v11.0;AttachDbFilename=C:\Users\sachin\Documents\Visual Studio 2012\WebSites\WebSite9\App_Data\Database.mdf;Integrated Security=True ");
        con.Open();
        SqlCommand cmd = new SqlCommand("Select * from admin where username='" + TextBox1.Text + "'",con);

        SqlDataReader rdr = cmd.ExecuteReader();
        if (rdr.Read())
        {
            TextBox2.Text = rdr[1].ToString();
            TextBox3.Text = rdr[2].ToString();
            TextBox4.Text = rdr[3].ToString();
           // TextBox1.Enabled = false;
            TextBox2.Enabled = false;
            TextBox3.Enabled = false;
            TextBox4.Enabled = false;
        }
        else
        {
            Response.Write("<script>alert('invalid username');</script>");
        }

        con.Close();
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(@"Data Source=(LocalDB)\v11.0;AttachDbFilename=C:\Users\sachin\Documents\Visual Studio 2012\WebSites\WebSite9\App_Data\Database.mdf;Integrated Security=True ");
        con.Open();
        SqlCommand cmd = new SqlCommand("update admin
 set password='"+TextBox2.Text+"',email='"+TextBox3.Text+"',city='"+TextBox4.Text+"'
        where username='"+TextBox1.Text+"'",con);
        cmd.ExecuteNonQuery();
        con.Close();

    }
    protected void Button4_Click(object sender, EventArgs e)
    {
        Button3.Enabled = true;
        TextBox2.Enabled = false;
        TextBox3.Enabled = false;
        TextBox4.Enabled = false;


    }
    protected void Button3_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(@"Data Source=(LocalDB)\v11.0;AttachDbFilename=C:\Users\sachin\Documents\Visual Studio 2012\WebSites\WebSite9\App_Data\Database.mdf;Integrated Security=True ");
        con.Open();
        SqlCommand cmd = new SqlCommand("delete admin  where username='" + TextBox1.Text + "'", con);
        cmd.ExecuteNonQuery();
        con.Close();
    }
    protected void Button5_Click(object sender, EventArgs e)
    {
        TextBox2.Enabled = true;
        TextBox3.Enabled = true;
        TextBox4.Enabled = true;
    }
}