In an effort to keep the upgrade process simple on a site, I want to only change as few files as needed. If all I want to do is change the header, footer and some graphics on the main page, and the width of the site, what files do I need?

I read the wiki and it says to copy the contents of the template_default which includes several folders and files. Do I need to have the folders "buttons, sideboxes, popup*, templates and all those files?

Or, can I just have the css, images folders?

Thank you for your help.