Modifying the Store Layout

I would like to modify the layout that appears when the Store Tab is displayed.  For instance, I would like to remove the UPCAID and Barcode fields.  I know how to change a layout, I just can't find the layout.  Would someone point me in the right direction? 

Also, could someone tell me how to designate my product "groups".  The layout allows me to Group my products, but each product then appears as it's own group.  I can't find anything on the products tab which allows me the identify or define a "group".