How does one change the maximum amount of items you can have on?

I was wondering if there's a wiki page/possibility that you can change the maximum amount of items you can hold in your backpack's bar.

I can't really describe it well in words, so here's the picutre I found on images.

http://www.rogomagazine.com/wordpress/wp-content/uploads/2014/08/Playerlist-backpack.png

I'm not really requesting for someone to script, I just wanted to know if it is possible to do so, and if there's a wiki page about it.

If I am not mistaken you just hit the ` button which is on the left of the number 1 on your keyboard.