[Theme: TwentyXS] twenty xs width

i have been unable to adjust the text container and header width of my website. After reading several posts on how to do this through editing the css or php, which i know little about, hence why am i using a wordpress site, i have had no success.

this is my website
http://www.andrewelman.com

i would like to adjust the width. I don’t really know how big to make it, but definitely wide enough to make it a majority of the page and minimize the margins. please take a look at my site and you will see what i mean.

please help

http://wordpress.org/extend/themes/twentyxs/