No need to pull the bed....thats too much work IMO if you're just alone doing it.
-Just use a 1/2" drive breaker bar
-you'll see my redneck stand setup
-floor jack under the pumpkin
-have the axle at full droop and then some while on the stands
-unbolt your shocks at the axle
-unbolt the highest bolt on both sides(the bolt that holds the shackle to the spring hanger
-i like to use my 1/2" drive 18" long craftsman ratcheting breaker bar because you cannot get an impact in there
-drop the axle down and let the springs pivot towards the ground(they'll do this on their own)
-then impact off the leaf spring to shackle bolt.
-install new shackles but leave shackle to leaf bolt just threaded on, not tightened.
-jack up axle
-bolt top of shackle to spring hanger, again, leave just threaded, not tightened.
-put truck on ground
-jump in bed and jump up and down a couple times
-torque bolts to proper spec aka tight as *****.
redneck jack setup: