Can someone help me? I seem to have gotten myself in a bit of a mess.

I have gotten too comfortable with my "go back to default" button and now made a slight coding change in the header template and now it won't let me get to the store at all (much less the admin area).
Is there a way to get an original and reload it via FTP? I tried to reload a version I had from a few days ago but all that did was throw another error. Maybe I am not doing it right?
site:
www.biz-plates.com/store
TIA for any help
