To make the right or left nav panels wider do the the following.
1. Under 'Master Settings' choose 'Edit Master Template'
2. Look for:
Left Panel Width
Right Panel Width
3. Click the 'Apply Style Changes' button
Doing this will effect how your category header images look. If you already have new images created then you can replace those. Do NOT make the changes if you don't have new images unless you know how it will look after.