Decrease width of illustrar theme

Hi,

I am working on this website: http://new.handymanbananas.com/

I am using the Illustrar theme.

I would like to decrease the site width. Spedifically, I would like there to be less white space on the sides of the site. The margin is too great.

Thank you for your help! I so appreciate it.
-Brittany