Modifying web site, PHP (+ a bit of js, ajax)

Hi, I have a web site built from off-shelf script. I need to modify few things and I don't know how. Please see url in attachement. To begin with, I need to do the following: - to fix download counter (with free downloads counter does not display real numbers) - to fix number of files displayed in the category view (it the number of files in category view does not "consider" that files are deleted and keeps counting up - upload form modification (include "free download" check button, include text message field) - review field needs to be visible at all times, even when empty - fix paypal gateway which sends confirmation message before the item was paid for. I will need more work eventually with winning bidder (direct work, payment with paypal or similar)