Change logos for individual forums

[The Big Three]

I'm wondering, how can I change the logos for each of my forums? My website is a sports discussion site, and we want to get team logos next to each of the team forums. Here's what it looks like now (cut out the stuff around it):



We want the pictures to replace the little basketballer image, something like OTRBasketball.com or NBADimensions.net has it.

Please be as detailed as possible in your explanation, I'm still inexperienced at administrating a site, so what might be simple for you probably isn't for me.

Is there a specific mod I need to upload?

Thanks in advance.