How do I manage profiles using SimpleMembership?

They made it easy to modify the profile with SimpleMembership. SimpleMembership is using the code first EF model and the user profile is defined in the file AccountModels.cs that is generated as part of the Internet template for MVC 4. Just modify the class UserProfile and add the new fields in the class definition. For example, adding a field for email would look something like this:

[Table("UserProfile")]
public class UserProfile
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int UserId { get; set; }
    public string UserName { get; set; }
    public string Email { get; set; }
}

Here is an example on how you would access the email field:

var context = new UsersContext();
var username = User.Identity.Name;
var user = context.UserProfiles.SingleOrDefault(u => u.UserName == username);
var email = user.Email;

Here is what the database looks like after adding the email field.

There is a good blog that describes some of the changes in SimpleMembership here. You can also find more detailed information on customizing and seeding SimpleMembership here.