I you use the manual update to Atahualpa as explained elsewhere on this forum you can always go back to the version you have if there is an issue. What I would do in your situation is.
- Backup your site files and database
- Upload the atahualpa351 folder to the wp-content/themes folder (don't activate yet)
- Apply bug fixes to the indicated files per the New Versions and Updating forum
- Copy any images you uploaded from the current Atahualpa images, header, and favicon folders to the new atahualpa351 images, header, and favicon folders.
- Activate the theme and take a look. If not working switch back to your previous version and troubleshoot.
- Once the new theme is activated make any path changes for background images, etc. in the Atahualpa Theme Options.
- If all looks good update all plugins and then update WordPress
This is a lot easier to do than it looks but I have done quite a few so who am I to speak. So take it slow, read the updating forum as referenced above, don't click before you thinks and ask any questions you have during the process. It's a great learning process.