Thank you for your purchase! To change the Facebook button to a Google + button you need to navigate to the following file...

theme_darkwall -> themes -> darkwall -> elements -> social.php

In this file you can change the "f" to a "g"... This should change the logo to a Google Plus logo. In this file you can also change the url (http://www.facebook.com/) to your liking so it points to your Google Plus profile! (http://plus.google.com/)

I hope that helps, let me know if you need further assistance.

b-lew