The easiest way to find out how much RAM your GS has is to select "About this Apple IIGS" under the Apple menu in GS/OS 6.0.1, if you've got GS/OS up and running yet.
Your next option is to turn on the GS and then press Control+Open Apple+Escape. That will bring up a page where you can enter the Control Panel. Highlight the Control Panel and press return. From there highlight RAM disk and press return. This will bring up a screen where you can set up a RAM disk. This page will tell you how much total RAM you have installed.
Hopes that helps,
Magnus