What are the mail files to modify for customizing

I purchased the software to manage our product category in our website. What are the main files to modify so I can get the app customized to match the rest of our website.



I need



[url]http://welmed.us/cat/index.php?subcats=Y&status=A&pshort=Y&pfull=Y&pname=Y&pkeywords=Y&search_performed=Y&cid=1&q=&x=16&y=6&dispatch=products.search[/url]



to look more like



[url]http://welmed.us/kmitac/category.php?category=2&pageno=1[/url]



any help will be appreciated.



I got some doc from CScart but I cant seem to make the changes I need to make.