For pages, you would be focusing on these theme files:
front-page.php
page-right.php
Open them and change the span8 class to span9, then look for the class span4 and change that to span3. This is so the main content part and the sidebar totals 12 columns wide:
span9 + span3 = 12
This will give you a smaller width on your sidebar, but then adds more to your main content.
Make sure you use a child theme for modifications so you can keep getting theme updates and not lose your changes. This theme has a folder in it “child-theme” which has a child theme that you can install and use. Please note when you activate this, you will need to redo your theme option settings because WP will see this as a new theme activation. But it will allow you to make custom changes. You would upload a copy of the two template files listed above into the same location as they exist, but put it into the child theme in a folder named: page-templates