Hi,
Don't be scared, all you need to do is, sit and spend some time on it. Trust me, it is not very challenging thing to take care. Don't forget to backup the PHP files that you make any changes in case of any failure.
I am afraid; this is considered as 100% custom modification and we don't provide free support or step-by-step instructions for custom coding modifications.
You may purchase premium support:
www.flexiblewebdesign.com/premium-support
and let us take care this modification for you directly on your website though.
Regards.
Support