Hover your mouse over the "handle" on a particular toolbar, and right click. You'll see a menu that has an entry for each toolbar, with a checkbox next to it. There will also be a submenu named "Button Heights", where you can pick a height between 12 and 60 pixels for that toolbar. (I think the default is 18 pixels.) Each toolbar (except for the Piano) can be separately sized.
Enjoy!
Mike
P.S. It is generally considered rude to discuss the size of your toolbar in public.