sheet metal thickness

I've attached a part which we got from an outside vendor.  The thickness of the sheet metal is set at .375", and I need it changed to 1/4", however, I can't figure out how to change it.  The person(s) who built the model apparently made a concerted effort to model EVERY part so that they are the most difficult to change, but this one has me completely buffaloed... HOW do I change the thickness??? 

SolidworksParts And Features