Creating a space between header and blog

Hi

I'm trying to create a space between the header and the beginning of the blog post - i think its probably an edit in the stylesheets, but I don't know what to edit it to and which one (assuming its single.php

You can view the posts here - http://cg-remaps.co.uk/stage-1-software-for-the-1-6-cdti-biturbo-engine/

Thanks
Farzan