Post body width – how to make it wider?

Hi everyone!

I’ve very recently joined WordPress.org and I’m still trying to get used to the way it works (after years using blogger.com).

I’m customising my blog having as base the theme Forefront.
I’ve been trying to make the posts area wider, even if the sidebars get a bit smaller.

Any help please?
I can’t really get to it.
URL: http://nourjournal.com
(without the “www.”)

Many thanks for any help!