Modification of old version of OS Commerce

I want to change some of my product pricing and shipping pricing to be reflected and processed in the shopping cart. My site uses an old version of OS Commerce, which was extensively modified by the original web designer (who is no longer in busiess). I have a friend who knows web design, but he told me that the things I want to be modified are so deep in the database that he could not find them in order to modify them. So, what I need is a person with extensive experience in OS Commerce that could go in and do the mods I want.