As with all coilovers you adjust the height by screwing up/down an "adjustor ring" (for want of a better description) along a threaded tube: Thus going lower will compress the spring a little, and raising the car has the opposite effect. In the pic above, the adjustor ring is the purple bit in the middle of the coilovers(touching the bottom of the coils). Coilovers are really meant for track use, as you can if needed for a certain track raise/lower the car to suit. For a road car you'll probably just pick a height that suits you and stick with it- unless for shows you wanna slam it that extra bit.