You can create a custom Editor Template. In the folder EditorTemplates under Views/Shared, add a view that has the name of your model. When you use pop up editing, it will use the template you defined.
Telerik has an example project demonstrating how this is done: Custom PopUp Editor Form.
Here is the code for an Editor Template I made for a project where my model was Tasks:
@model Whiteboard.Models.Tasks
<fieldset>
<legend>Tasks</legend>
@Html.HiddenFor(c => c.TID)
<div>
<p>
@Html.LabelFor(w => w.Task):<br />
@Html.TextBoxFor(c => c.Task, new { style = "width: 375px;" })
</p>
</div>
<div>
<p>
@Html.LabelFor(w => w.WDate):<br />
@Html.EditorFor(c => c.WDate)
</p>
</div>
<div>
<p>
@Html.LabelFor(w => w.Description):<br />
@Html.TextAreaFor(c => c.Description, new { cols = "45", rows = "15", @class = "ext_TextArea" })
</p>
</div>
<div>
<p>
@Html.LabelFor(w => w.Notes):<br />
@Html.TextAreaFor(c => c.Notes, new { cols = "45", rows = "5", @class = "ext_TextArea" })
</p>
</div>
</fieldset>