// 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");
}