Change amount posts shown on each page

The amount of posts that can be posted onto a single page on our site is set to 7. This amount is perfect for our homepage but not for some of our other category pages.
ow can we set each of our category pages to show a specified amount of posts onto the page? If there is some form of code needed to do this what would it be, and where would it need to be inserted? (have 0 amount of coding knowledge)

Thanks
http://madassgamers.com/