Need help with resoring website to any previous version!!!
 

first time on forum here and not an IT person with a basic question....
I had been using Tarski and then switched over to Atahualpa. A notice in the web manager pages of the site appeared that a new version of Tarski was available. Long day and my concentration was not great and I forgot I was now using atahualpa so I clicked on the upgrade for TARSKI.
RESULT? Everything I've been working on for the past six months to style/tinker with the appearance and aspects of the website with side bars, flash headers, links, etc.,. is now all gone. I'm not even sure whether the site is using tarski or atahualpa at this point. It's barren and looks like it did the first day I started creating the site...
I have no idea how to get the site back to how it was a few hours ago and if that is even possible. ANY help would be greatly appreciated! MY site is in shambles right now. Just a bare site with only the middle column still having some writing.

Upgrading another theme should have no effect on Atahualpa. Which theme is shown in the theme switcher for WordPress? If you upgraded Tarski and then said activate after updating you may be able to just go to Appearance>Themes and activate Atahualpa to get back to where you were otherwise it might requite restoring a backup. Do you have any kind of backup?