When dealing with Rockbox, whether upgrading the build, bootloader, or theme, it's best to do the following so that you can see everything you need to work with.
Copy and pasted from the Gigabeat Port Wiki:
* (For Windows) In Windows Explorer, navigate to the "Tools" menu -> select "Folder Options."
* Click the "View" tab.
* Check "Show hidden Files and Folders."
* UNcheck "Hide Extensions for known file types"
* UNcheck "Hide protected operating system files."
* Click "Apply."
* Click "Apply to All Folders."
The only folders pertaining to Rockbox that should be in the root of your player is the .rockbox folder. Music and Playlists may also be there along with any other folder that you may have created, but the one important to how Rockbox works is the .rockbox folder. If you see anything outside of that folder, the extraction didn't go as planned and you should move those folders back into the .rockbox folder. (ie folders named themes, wps, fonts, background, etc.) Please make sure you agree to overwrite if prompted to when you copy or extract things into the .rockbox folder.