update database with edit textbox value clicking button

protected void Page_Load(object sender, EventArgs e)
        {
            Dictionary<string, string> dct = CUser.GetUserInfo();
            tbxFirstName.Text = dct["FirstName"];
            tbxLastName.Text = dct["LastName"];
            tbxEmail.Text = dct["Email"];
            tbxPhone.Text = dct["Phone"];
            tbxPassportNumber.Text = dct["PassportNumber"];
            tbxUsername.Text = dct["Username"];

            if (!Page.IsPostBack)
            {

            }
        }

        protected void btnSave_Click(object sender, EventArgs e)
        {
            CUser cUser = new CUser();
            cUser.FirstName = tbxFirstName.Text;
            cUser.LastName = tbxLastName.Text;
            cUser.Phone = tbxPhone.Text;
            cUser.Email = tbxEmail.Text;
            cUser.Username = tbxUsername.Text;
            cUser.PassportNumber = tbxPassportNumber.Text;
            cUser.Attach();

            if (!cUser.Save())
            {

            }
        }
    }
}

public bool Save()
 {
     try
     {
         using (var db = new MiniFootballEntities())
         {

             db.Users.AddObject(entity);
             db.SaveChanges();

             return true;
         }
     }
     catch (Exception err)
     {
         return false;

     }
 }
 public void Attach (User user)
 {
     using (var db = new MiniFootballEntities())
     {
         db.Users.Attach(user);
         db.SaveChanges();
     }
 }
 public static Dictionary<string, string> GetUserInfo()
 {
     try
     {
         using (var db = new MiniFootballEntities())
         {
             var data = db.Users.First();


             Dictionary<string, string> dct = new Dictionary<string, string>();

             dct.Add("FirstName", data.FirstName);
             dct.Add("LastName", data.LastName);
             dct.Add("Email", data.Email);
             dct.Add("Phone", data.Phone);
             dct.Add("PassportNumber", data.PassportNumber);
             dct.Add("Username", data.Username);
             return dct;
         }
     }
     catch (Exception err)
     {
         return null;
     }
 }