Put your truck on jackstands!!!!!
Remove the wheels. put your jack under the rear differential.
unbolt the rear swaybay.
Unbolt the bottoms of the shocks.
lower the jack/differential slowly until the springs are loose enough to fall out.
remove the springs and put the new springs in their place.
take a hacksaw to your bumpstops and cut them in half at the crease in the middle.
raise the differential up slowly and seat the springs in the cups.
bolt everything back up.
If you have any questions just PM tybardy. do the exact opposite of what he tells you to do. (I thought the cheap shots on tybardy would get old quick... but no so far
)
Unfortunately, the truck probably wont lower at all unless you get some new shocks. I had the 3" eibachs with shock extenders and it only lowered the truck about 1/2" until i replaced my shocks.. then it was a full 3". Good Luck.