Not hard at all. I lowered mine all by myself. It took me about an hour and a half for the front springs. I also replaced my front shocks at the same time. It wouldn't have taken that long had I not had to build the damn shocks!
There is NO need for a spring compressor. All you need to do is use another jack under the control arm and slowly release the pressure on the spring. The spring simply sits in sort of a cupped out area in the control arm. It's nothing like a strut, in which you do need a compressor.
The rear is straight forward. Shackles are a breeze. Now the hangers are a different story. Make sure you have an air chisel or a good drill bit to remove the factory rivets holding the factory hangers in place. The first truck I did it took like 2 hours to get the studs removed. The next one I did they came right out.
Good luck and make sure to replace your shocks as soon as you can, along with an alignment.