How to use code first migrations to update a database?
<p>I made a c#.NET WebAPI and it worked, but when I changed the model it stopped working and it gives me the following error message.</p>

<blockquote>
  <p>The model backing the 'ApiDbContext' context has changed since the
  database was created. Consider using Code First Migrations to update
  the database.</p>
</blockquote>

<p>This is my code:</p>

<p><strong>The Model (unchanged):</strong></p>

<pre class="lang-cs prettyprint-override"><code>using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Test.Models
{
    public class User
    {
        public int Id { get; set; }
        public string Name { get; set; }
        //public DateTime startTime { get; set; }
        //public DateTime endTime { get; set; }
        //public int Age { get; set; }
        //public string Adress { get; set; }
    }
}
</code></pre>

<p><strong>The Model (changed):</strong></p>

<pre class="lang-cs prettyprint-override"><code>using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Test.Models
{
    public class User
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public DateTime startTime { get; set; }
        //public DateTime endTime { get; set; }
        //public int Age { get; set; }
        //public string Adress { get; set; }
    }
}
</code></pre>

<p><strong>The Controller (changed at updateUser):</strong></p>

<pre class="lang-cs prettyprint-override"><code>using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using Test.DBA;
using Test.Models;

namespace Test.Controllers
{
    public class UserAPIController : ApiController
    {
        ApiDbContext dbContext = null;
        public UserAPIController()
        {
            dbContext = new ApiDbContext();
        }
        [HttpPost]
        public IHttpActionResult InsertUser(User user)
        {
            dbContext.Users.Add(user);
            dbContext.SaveChangesAsync();

            return Ok(user.Name);
        }

        public IEnumerable&lt;User&gt; GetAllUser()
        {
            var list = dbContext.Users.ToList();
            return list;
        }

        [HttpPost]
        public IHttpActionResult DeleteUser(User user)
        {
            dbContext.Users.Remove(user);
            dbContext.SaveChanges();

            return Ok(user.Name);
        }

        [HttpGet]
        public IHttpActionResult ViewUser(int id)
        {
            var student = dbContext.Users.Find(id);
            return Ok(student);
        }

        [HttpPost]
        public IHttpActionResult UpdateUser(User user)
        {
            User std = dbContext.Users.Find(user.Id);

            std.Name = user.Name;
            std.startTime = user.startTime;
            //std.endTime = user.endTime;
            //std.Age = user.Age;
            //std.Adress = user.Adress;

            dbContext.Entry(std).State = System.Data.Entity.EntityState.Modified;
            dbContext.SaveChangesAsync();

            return Ok();
        }
    }
}
</code></pre>

<p><strong>DBContext:</strong></p>

<pre class="lang-cs prettyprint-override"><code>using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data.Entity;
using Test.Models;

namespace Test.DBA
{
    public class ApiDbContext :DbContext
    {
        public ApiDbContext() : base("Connection")
        {

        }
        public DbSet&lt;User&gt; Users { get; set; }
    }
}
</code></pre>

<p><strong>Connection string:</strong></p>

<pre class="lang-cs prettyprint-override"><code>&lt;connectionStrings&gt;
   &lt;add name ="Connection" connectionString="Data Source=.\SQLExpress;Initial Catalog=k;Integrated Security=True" providerName="System.Data.SqlClient"/&gt;
&lt;/connectionStrings&gt;
</code></pre>