All Righty, then!
Those are easy and reasonably safe to adjust (unlike the ones that I have that try to take your finger off!)
Looking at the picture, you have a stud projection at about 2 o'clock with a couple of locknuts on them, and a bolt at about 6 o'clock, also with a locknut on it.
It is best to raise or lower the car when it is sitting normally on the wheels. It is also important to have rolled the car for 10-20 feet before you start to make sure the suspension has settled (if you've been out driving and pull into the garage and then do not jack it up at all, you're all set. The same holds true if you just drive it up onto ramps or onto a drive-on lift).
On the 2pm studs, loosen both nuts about 1 turn each. If the stud has a hex hole in the end of it, use a hex wrench to keep it from moving. DO NOT LOOSEN THE STUD - JUST LEAVE IT THREADED IN!
Go to the 6pm bolt and loosen the locknut. To lower the car, loosen the bolt (turn counter-clockwise), thereby allowing the 2pm stud to move downwards. This allows the wheel trailing arm ends to move upwards, while the car moves downwards (Use your forearm pivoting around the end of your upper arm to get the picture, or draw a stick drawing of the suspension to get the idea). It may take a turn or two to get it down where you want it.
When you get it to the height you want, re-tighten all of the locknuts.
You're done.
gn