If you have the auto leveling suspension, you need to change the rods to the sensors or bend them depending upon the kit.
I did the Eibach kit last Saturday. The rears are super easy to do, you just need to be careful not to stress the ABS sensors. The fronts are a bit more involved b/c the spring is part of the shock but they are still not that hard to change.
The Eibach kit consists of just new springs, sensor rods, and bump stops for the front.
There are other kits, I can just comment on the one I used.
If you lowered it and didn't like the way it looks, you can easily swap it back to stock.