How to change container size?

Hi! Im working on my site http://www.johnschuette.com. The theme is Hatch.
I’d like to change the container size to add responsive images and slide shows. My images are 1024 wide and the themes containers are something like 500 wide.
I have tried to find the CSS code (not that I know what to do with it) but havent been successfull.
Can anyone give me some support on this?

Many thanks!