Expanding the product to fill page

[buddhajewelry]

Hello,

 

Usually I can find how to fix my issues by searching but I'm not having any luck with this one. This is my first time posting and I'm not HTML savvy. I'm blindly putting together this site.

 

I'm not going to use any of my side layers except the catalog one I have in use already. What I would like to do is expand the grid for products to fill the page from side to side (maybe 4 per row) instead of having only 2 per row with the sides empty and white (see attached screenshot).  Can this be done and how would I do it?

The more information and detail you give me the better. Like I said, I have 0 HTML schooling and have just been googling everything. 

THANK YOU!!