Do not use cPanel on the servert to edit the file. If you don't know what you are doing you could break the file. Download it by ftp and keep a copy safe as backup.
Here is one edit you can try. Open the original on your PC in a good editor such as NoteTab Lite and locate this code towards the end of the template.
<tr>
<td><?php echo $payment_info_details ?></td>
<td><?php echo $shipping_info_details ?></td>
</tr>
</table>
and then add another row in the table and enter some text. For example:
<tr>
<td><?php echo $payment_info_details ?></td>
<td><?php echo $shipping_info_details ?></td>
</tr>
<tr><td colspan="2">
<p> this is some new text.</p>
</td></tr>
</table>
Save the file, upload to the server & test. I'm not sure if that is the right place to edit, but that is the sort of thing you need to do. This is not "new code" but XHTML which has been around for years.