How to make my BigCartel shop wider?

Hi!

I've been trying a lot to make my Bigcartel shop wider but it's no use. I don't know where (CSS doc? HTML pages?) to change (or add) the pixel width and the photographs of my products are all messed up in the shop at the moment.

This is my URL http://gallanttales.bigcartel.com

I'll love to show my products in a wider layout. I found this "expanded" bigcartel design that might work as a reference: http://shop.ugmonk.com

I'll be immensely happy to receive any clue,

Thank you all in advance! ^_^