Good morning Sarah…. straight to the point, doing what you described above would actually cause a lot of layout problems and I would not attempt that. Because you are wanting specific widths, this won’t be possible because this theme uses the Twitter Bootstrap framework which has a “specific” layout with specific sizes. Changing any of the sizing would cause way too many issues.
The only way to adjust the widths of columns is to go into the theme files and change the span classes as I mentioned earlier in the post reply. The files in question would be the page templates, but if I understand correctly, you are referring to the Left + right layout? The template for this would be the “page-left-right.php” file. You would need to change the spans:
Left sidebar = span3
Main Content = span5
Right sidebar = span4
You would need to change these spans (the number part) to adjust widths which you have from span1 to span12 to use. The span12 is full width, while the span1 is 60px.
If you open the theme’s style.css and look around line 2277, you will see the span sizes from .span12 down to span1.
For your left sidebar, if you want it to be 160px, the closest span class would be span2 (140px) or span3 (220px). These spans also have a margin which is 20px each side (left and right).