I just did a find and replace on everything that said 520 (the width of content) and replaced that with 800. This is the result.
As you can see the top and bottom of the content areas are actually a image. Just changing a couple of numbers can’t really help with that. You would need to redo the images. (or you could just take them out) Like I did here
This looks a little better.
Code is here if you want to use it.