Increase Sidebar Width

Greetings,

I need to increase the sidebar from 288 to 300px wide on the SilverOrchid theme. I would like to do this by decreasing the small blank areas on the left and right, not by decreasing the area for the post content (sorry if I am not using the proper terminology. I am self-taught when it comes to working with wordpress and not familiar with all the terms). Could someone help me out by pointing me in the right direction? I’d be most appreciative.

Also, the reason for this is to post a 300×250 item in a sidebar text box widget. Will I need to alter the widget as well? Meaning, are text box widgets set to allow for the max width of the sidebar or will it have its own properties I need to alter?

Thank you everyone for your help.

Here’s a screenshot of exactly what I am referring to:
http://ignorethelies.com/wp-content/uploads/2013/06/ignorethelies_screenshot.jpg

Here’s the website itself: http://ignorethelies.com