By clicking on the arrows of the cabinet that are placed in the designer, the size of the cabinet is able to be changed by dragging and dropping to the dimensions you would like. This feature has to be enabled under the Drag Resizing option.
First you'll need to enable this new function in your catalog settings under "common" settings.
Then you click on a cabinet in the designer, you'll see the new arrows you can grab and drag to resize the cabinet in any direction!