Drag-and-drop editing of Layout Dimensions

I was reading the theme description and it says there’s a ‘drag and drop’ section in ‘theme options’ where you can change the width of your columns etc. There isn’t one for me. I can choose the layout (1,2 columns, left, right etc) but that’s all.

Any idea where this would be and how I could increase the width of the right column so my ads fit correctly?

http://www.mmmboptastic.com

Thanks