The best way to test if your carbonation (and most fun way) is to taste it. If it is where you think you like it, drop the pressure down to a suitable serving pressure. Basically to where it pours nicely (generally 10-14psi depending on style). To release the pressure, there should be a little key ring on the lid of your keg. Turn the pressure down on the regulator, and pull that pin to let the pressure out of the keg. Then set the pressure on your regulator to serving pressure.