There are several ways, but here's how I do it (assuming springs with no military wrap and OE-type rubber bushings):
Lift vehicle by jacking up differential > Place jackstands under frame and let off jack until frame is on the stands, but keep a little tension on the springs > remove u-bolts (one side at a time if you wish) and then let off the jack until the spring unloads and the axle drops off the spring center pin. > remove bolts to remove springs > Drill 6 or 8 thru-holes in the old spring eye bushing rubber to relieve some tension in the bushing. > Drive out the bushing center sleeve > The outer steel bushing sleeve can be cut using a hacksaw or die grinder in the slot where the main leaf wraps around the sleeve and back onto itself (careful not to damage the spring itself) > Once the outer sleeve is cut, just use screw drivers or whatever you can to start folding it in on itself until jou can drive it out of the spring eye.
Installation is straightforward, and a piece of cake if putting poly bushings in it. U-bolt torque is a controversial topic. Some say all you can get, some say around 150 ft-lbs. Either way, check them frequently after you install them and retorque several times, driving for a day or two in between. Do this until they no longer need to be re-torqued after driving.