I'd also like to stress backing up your site, before any modification, style change, or code edit. Backup all files that you will work with so that you have a revert point. Also, backup your site at least once a week minimally. Mor often if possible. I try to do it daily. you can hit backup and go to sleep but backups have saved me a few times. If you're looking to edit the footer page it's overall_footer.tpl in w/e theme you want to edit it in. HEader is overall_header.tpl, be sure to use comment tags so that you will remember what you did at a later date!