If You want to update from Quick.Cart v3.5. Check changes using program Total Commander. Select file in Quick.Cart v3.5 (first column) and the same file in Quick.Cart v3.6 (second column) and click in menu "Files" > "Compare by Content". You will find changes made by us.
HOW TO UPDATE FROM v3.4? You must first update to v3.5 http://opensolution.org/Quick.Cart/forum/?p=readTopic&nr=6618