How do I update existinf records in my edit action method on the controller

HTTP Error 404.0 - Not Found
The resource you are looking for has been removed, had its name changed, or is temporarily unavailable.

if (StuEdit == null) //it displays an empty view on the web browser
{
   return HttpNotFound();
}

using LinkViewStudentDb.Models;
using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace LinkViewStudentDb.Controllers
{
    public class HomrController : Controller
    {
        //
        // GET: /Homr/
        UserDb us = new UserDb();
        public ActionResult Index()
        {
            return View();
        }

        public ActionResult ViewAllStu()
        {
            UserDb us = new UserDb();
            var stuCol = us.Students.Select(st => st);
            return View(stuCol);
        }
        public ActionResult create()
        {
            return View();
        }

        [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult create(FormCollection form)
        {
            var StuCre = new Student();

            TryUpdateModel(StuCre, form.ToValueProvider());


            if (ModelState.IsValid)
            {
                us.Students.Add(StuCre);
                us.SaveChanges();
                return RedirectToAction("Index");
            }
            return View(StuCre);
        }


        public ActionResult edit(string id = null)
        {
            Student StuEdit = us.Students.Find(id);
       
            if (StuEdit == null)
            {
                return HttpNotFound();
            }
            return View(StuEdit);
        }
        [HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult edit([Bind(Include = "StuID, name, Surname, age,sex")]Student StuEdit)
        {
            TryUpdateModel(StuEdit);
            if (ModelState.IsValid)
            {

                us.Entry(StuEdit).State = EntityState.Modified;
                us.SaveChanges();
                return RedirectToAction("Index");
            }
            return View(StuEdit);

        }
    }
}