thereyoflite on "How to Change the Width of Content Section in Theme?"

Hello Everyone. I want to insert a 720x90 ad in the middle of each post, but my theme is too narrow. How can I change the width of the content section, without changing the sidebar? I also don't want to ruin the appearance of my site. Thanks!
The Site is http://oneclickshutter.com/
the theme is the Max Magazine Theme