Upgrading Worpdress after modifying current version
I'm having to tweak the current version (3.0.2) to suit my requirements. Currently I've made changes to the CSS, sidebar_gmap.php file as well as changing occurrences of the word "Poster" and replacing for "Seller". What I'd like to know is when upgrading to the latest versions in the future how will this affect things? I.e. when upgrading will I lose all the tweaks I've made or is only a couple of files that actually get changed in the upgrade?