Be careful before you commit to doing anything in "Editor" ... it is editing the actual theme files, you should always have a backup of your theme ready to switch to in case you fudge it up.
Have you ever made a backup of your theme? If you can get into your site by FTP, you will be able to find a folder containing all your theme files. Download that to your local computer for safekeeping, make it into a ZIP file to make sure you don't mistakenly edit those files anymore.
I am a little short on time to explain it now but I think this guy explains it well: