The lower spring perches can be unscrewed a few turns to lower the car. You can't do this with the tires bearing weight. Most of us who have experimented with lowering agree that about 3/4" (19mm) is as far as you should really go. Measure this from a frame hardpoint near the tires, not bodywork. Lowering changes something called "bump steer curves" and corner weights. If not checked & readjusted, they can lead to squirrely handling. The average alignment shop will probably be capable of checking bump steer, but not necessarily competent. Corner weights are checked with scales. Seek out serious racers.
The shocks are also externally double-adjustable for compression and rebound. This affects comfort and handling. Keep good notes and be methodical.