If you edit and tweak a theme, making the changes in the theme’s folder, all changes will be wiped out if you upgrade the theme.
If you want to keep your changes, and never upgrade your theme, you can make it yours by changing the theme name.
to do this:
- Set your WordPress site to another theme, like twenty-ten
- FTP into Root -> wp-content -> themes ->
- Rename your edited theme to anything
- Go into the directory and edit ‘style.css’ – adding the theme name
- Then refresh your WordPress theme selection page and re-add your newly renamed theme
Now you won’t get prompted to update your theme.