title: How to rename a file using NSFileManager
body: <p>I have a single file named <strong>a.caf</strong> in the documents directory. I would like to rename it when user types into a <code>UITextField</code> and presses change (the text entered in the <code>UITextField</code> should be the new filename).</p>
  
  <p>How can I do this?</p>