$("#ddl").change(function () {
            var ddl = this;
            $.ajax({
                url: "SelectedChange",
                type: "POST",
                data:
				{
				    'id': ddl.options[ddl.selectedIndex].value
				},
                contentType: "application/x-www-form-urlencoded; charset=UTF-8",
                success: function (data) {
                },
                error: function (error) {
                    alert(error);
                }
            })
        });

@using (Ajax.BeginForm("TestAjax", new AjaxOptions { HttpMethod = "Post", UpdateTargetId = "textEntered", OnFailure = "PostFailure", OnSuccess = "PostSuccess", OnComplete = "PostOnComplete" }))
    {
        <div>
           @Html.LabelFor(m => m.UserName)
           @Html.TextBoxFor(m => m.UserName)
        </div>

        <div>
           @Html.LabelFor(m => m.Password)
           @Html.TextBoxFor(m => m.Password)
        </div>

        <div>
           @Html.LabelFor(m => m.EmailAddress)
           @Html.TextBoxFor(m => m.EmailAddress)
        </div>

        <input type="submit" id="submitForm" value="Submit Form" />
    }

    <div id="textEntered">d</div>