make content on site wider

Hi,
I am sure this is answered somewhere, but have not been able to find it.

I would like to widen the content area for my site(s). Most use Weaver. Here is my site:
http://www.reelingsilk.com/academy/

As you can see, I was able to widen the header area, but not the content area.

Any help? And, is there something available, similar to the old dreamweaver properties, where I can make the width of the site responsive to whatever screen it is viewed on? I don’t mean on iphones or ipads; I mean, on computer screens. Is there something that would make it adjust automatically? I sort of hate the wasted space on both sides.

Thanks in advance,
Debbie