Hi, it's me again!
You use this osc design from Template Monster, or your web guy did it himself?
The alignment look nice, and it's hard to get it align in order.
You want to change link, first you have to find where that image is inserted. The image url is http://www.sudburydiamonds.com/shop/images/m11.gif. So a sure bet is that the image is insert at /shop/index.php.
Then look for <a href ></a>. I think that image is within <a href></a>. You'll change the url from there, like: <a href="http://www.sudburydiamonds.com/shop/index.php?cPath=45"><img src="images/m11.gif"></a>
Reply me if I'm right or wrong.