This is an easy repair. The hardest part is getting all the bolts loose. There are 2 different ways to do this, one is to completely remove the axle, i.e. disconnect driveshaft, brakelines, ebrake cable, shackles. The other is to do it under the vehicle, using a set of straps/chains to keep the axle up, by only removing the rear springs.
If you are putting in new packs both sides need to be done.
You will need lots of penetrating oil for this. Start now by spraying the oil on the axle U-bolts, shackle bolts and allow time for it to do its job. Make sure to support the truck properly with jack stands, safety first. Spray the oil again. Remove the tire. Use a ratchet strap or chain to support the axle near the U-bolts, along with supporting the axle with a jack stand. Right now, the leaf spring should have no tension/weight on it. Undo the rear shackle bolts. Remove the front eye bolt, marking this as the front. Now the spring/axle is loose from the truck. Now, using a 1/2" or larger impact wrench remove the U-bolts. Installation is reverse of removal.
At this time, you may want to replace all the bushings in the spring pack, if they are worn.
If you are replacing a single spring in the spring pack, there is a bolt through the middle of the pack, spray penetrating oil on this and wait a few, then remove the nut, make sure to place the springs down to remember which way they came off. You may have to replace the bolt/nut on the spring pack. Reassemble.