Hi @display-advice
First of all WOW, you have a great site there and I can see how much thought has gone into this 🙂
Before performing any updates like this it is vital that you fully back up your site should you need to restore it again, here is a link to the WordPress Codex showing you how to do this yourself (there are also plenty of plugins and tutorials out there as well for this ) http://codex.wordpress.org/WordPress_Backups
I am not sure how your theme will perform against the update but as a first thought it is not that much of a jump between versions so I wouldn’t think anything drastic would happen.
As this is an eCommerce site creating income it would be a very good idea to have a local copy of this and the database so you can test out updates like this before actually doing it on the live site. This way you are able to find any issues before going live. If you are not sure on how to set up a local installation of WordPress then this tutorial walks you through step by step 🙂
http://wpmu.org/install-wordpress-locally-on-windows-with-xampp/
Also the developer of this theme might mind it helpful viewing the change logs between WordPress version, for your convenience here is the link http://codex.wordpress.org/WordPress_Versions
Hope this helps guide you in the right direction?
Cheers
