Reference: http://www.dynamicdrive.com/dynamici...ddmegamenu.htm (the link is broken in the opening post)
You can name the files anything you like - "mystyles.css" and "myscripts.js", for example, as long as what's inside remains unaltered.
You would then need to update the links to the revised file names in the <head> section of your website template;
and of course preserve reference to the copyright notice - I've just condensed the line for simplicity.
<link rel="stylesheet" type="text/css" href="mystyles.css" />
Your web host might be configured to cache CSS, js and images but you can normally pull through the files again with a hard-refresh (CTRL+F5 on PC). If that doesn't show the changes, you might need to empty your browser cache and/or temp Internet files.