Basically any video on YouTube will tell you how to adjust them, even the Tein specific videos or guides you find for Silvias should apply also as they pretty much mount in exactly the same way.
I like this method as it has a little more thought put into it instead of just using base adjustment to determine ride height. Basically you take the springs off and put the coilovers in the car, then put your wheels on, then jack the wheels up as far as they will go. If the wheels foul on anything (lock to lock included on the front) you adjust the base height until they don't. Then you put the springs back on the coilovers and adjust the spring seat collars to get your desired ride height.
Most of this won't apply to the rear because of the Commodore's separated spring/shock and swing arm setup.