If you use the link and password HoF gave you to login to the cPanel (where the file manager and everything is...NOT the one on the website itself! It should be the link that ends in a series of numbers) then you can scroll down and find phpmyadmin under the Databases section.
Next, once you're inside of phpmyadmin, you'll want to go to your database (which is probably something like sitename_mysidia), and then find adopts_useroptions on the side. Then find your account and click on "edit" beside it, and change the theme there to the name of a fixed theme (must be exact!).
Click here for a video showing just how to do this :)