Align entire site to the left

Hi,

Apologies for having to ask what is (hopefully) an easy question. I’ve just set up a blog and am using your Wilson theme. I’m new to wordpress and CSS coding in general, and I’m having trouble figuring out how to align the blog to the left. I want the left-hand navigation menu to sit on the left side of the screen, as compared to default where the navigation seems to have a margin of about 4 cm.

Thanks very much for your help and your theme!