How to save additional data in the database?

I am performing a user registration, but I am only able to save the Username and Password in the database. How can I save the LastName together?

Below is my controller with your Actions.

using ProjetoProtocolo_TCC.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Security;
using WebMatrix.WebData;

namespace ProjetoProtocolo_TCC.Controllers
{
    public class ContaController : Controller
    {
        // GET: Conta
        [HttpGet]

        public ActionResult Login()
        {

            return View();
        }
        [HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult Login(Login logindata, string ReturnUrl )
        {
            if (ModelState.IsValid)
            {
               if (WebSecurity.Login(logindata.NomeUsuario, logindata.Senha))
               {
                   if(ReturnUrl!= null)
                   {
                       return Redirect(ReturnUrl);
                   }
                   return RedirectToAction("Index", "Home");
               }
               else
               {
                  ModelState.AddModelError("", "Nome de usuário ou senha inválidos");
                 return View(logindata);
               }


            }
            ModelState.AddModelError("", "Nome de usuário ou senha inválidos");
            return View(logindata);
           // return Content(logindata.NomeUsuario + ' ' + logindata.Senha);
        }

        [HttpGet]
        public ActionResult Register()
        {

            return View();

        }

        [HttpPost]
        [ValidateAntiForgeryToken]

        public ActionResult Register(Register registerdata, string role)
        {
            if (ModelState.IsValid)
            {

                try
                {
                    WebSecurity.CreateUserAndAccount(registerdata.NomeUsuario, registerdata.Senha);

                    var MINHAVARIAVEL = registerdata.SobrenomeUsuario.ToString();
                    //{Preciso salvar no banco de dados o valor do sobrenomeUsuario , porem
                // o websecurity so permite eu salvar o Username e password , teria algum jeito de salvar
                // os demais campos?}

                    Roles.AddUserToRole(registerdata.NomeUsuario, role);



                    return RedirectToAction("Index", "Home");
                }
                catch (MembershipCreateUserException exception )
                {

                    ModelState.AddModelError("", "O Nome de usuário já existe");
                    return View(registerdata);
                }
            }
            ModelState.AddModelError("", "O Nome de usuário já existe");
            return View(registerdata);
          //  return Content(registerdata.NomeUsuario + ' ' + registerdata.Senha);
        }
        public ActionResult Logout()
        {
            WebSecurity.Logout();
            return RedirectToAction("Index", "Home");
        }

    }
}

This is my class that contains the information:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace ProjetoProtocolo_TCC.Models
{
    public class Register
    {
        public string NomeUsuario { get; set; }
        public string SobrenomeUsuario { get; set; }
        public string Senha { get; set; }
    }
}

It's a login code, in which I save the user's name and password, but I need to save more information as a surname, but I'm not able to