I have a Drop down mega menu using a CSS file and a HTML file. I want to use this instead of the drupal primary menu. I have been advised to change the HTML in the page-header.inc file but I don't know how to do this?

On looking at the page-header.inc file, do i place the code under the file or in the header? I have no idea! Do I have to change this section?

<?php print theme('links', $primary_links, array('class' => 'links primary-links')) ?>

any advice would be great, I'm a noob