sorting gridview in mvc4

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MVC4

Hi Everyone...........

In my program i am displaying the list of values in gridview like this........

@{
   var grid = new WebGrid(source: Model.ElementAt(0).users, rowsPerPage: 20, 
   canPage: true, canSort: true,sortFieldName:"UserName",defaultSort: "UserName");
 }
<p>
  <div id="grid">
    @grid.GetHtml(
    tableStyle: "grid",
    headerStyle: "head",
    alternatingRowStyle: "alt",
    columns: grid.Columns(
    grid.Column("UserName","User Name",canSort:true),
    grid.Column("Email","Email",canSort:true),
    grid.Column("Date","Created Date",canSort:true),
    grid.Column("DeptID","Department ID",canSort:true),
    grid.Column(format: (item) => Html.ActionLink("Details", "Details", 
     new { id =   item.UserID     }))
   ))
     </div>
  </p>

now i want to sort the values in grid view..... how can i do this....... can anybody help me