Linking image on main page to category pages

[Kenteman]

I have what I hope is a simple question.

I am trying to set up my site that that when one clicks on any category in my sidebar, the main image changes to an image which is related to that category. In addition, items in that category would open on that same page as well. How can I achieve this?

Here is my site

http://kente.midwesttradegroup.com/zcfkente/