Rear springs can be done easily, remove shocker, get mate to lever down the rear suspension arm, spring will prise out. New lowering spring goes back in easily, fit new shorter length shocker. Job done.

20 minutes.
Front springs, need some tools and some help really. Springs need to be clamped and compressed with spring compressors.
Method:drown all bolts etc with WD40 type stuff before you start, day before is better.
Jack up and support on stands, remove wheel.
Place jack under bottom of lower suspension arm and raise to take a bit of weight, not lifting the bus though.
Top shocker nut, clean threads of spindle with wire brush and plenty of WD40, undo nut while holding the centre spindle with a 6mm open-ended spanner or mole-grips. Once nut is undone enough to cover the 6mm flats area, it will either be free enough to unscrew easily, or you may have to grip the spindle below the nut to stop it spinning. Remove bottom shocker bolt and nut, watch for the split collar at the rear of the bolt-hole for dropping out and rolling away, it may come out, it may not. Get it out anyway. Shock will drop out the bottom.
Undo the two allen headed bolts that hold the top wishbone to the ball-joint, bolts will be tight and you must clean out the allen-head socket properly and use a decent allen-key and a pipe or preferably a 1/2" drive hexagon bit. If you round out the hole then mole-grips or saw off the bolt heads and sort the problem out after. If ball-joint if knacked, then replace now.
Lever the wishbone up enough to clear the ball-joint. Lower the jack off lowering the bottom wishbone. Stub-axle and disc assembly will now be free to drop away, DON`T let it stretch the rubber brake pipe, tie it back with something.
Put 2 spring compressors onto spring diagonally opposite each other and wind enough compression onto the spring to allow you to get the spring out, mate needed to lever down the bottom wishbone while you prise out the spring CAREFULLY, don`t forget the power of that spring if it gets loose
Clean spring seat and top rubber seat. Tape the rubber to your new spring in a couple of places to stop it falling off. Assemble spring compressors to new spring after releasing from old spring CAREFULLY. Wind on enough compression to get new spring into place, should be easier as you have a shorter spring now. May even get it in with mate levering down on the bottom wishbone. Once the spring is in place and SEATED in correct position with the ends in their respective grooves place jack back under the bottom wishbone and raise to take a bit of weight onto the spring, NOT enough to lift it off the stands!
Remove the upper bump-stop/shock cover from the old shocks, shorten the bump-stop rubber by 2 grooves if you are lowering by 40mm or more. Fit the cover/bump stop to the new shock. Fit new shorter shocker from the bottom, Note that split collar goes at the back on the bolt, this takes up any space between the bottom shocker mount bush and the wishbone. Locate spindle through the top mount hole and add nut, make sure you get all the top spacers and rubber in position as it came off.
Check top wishbone for any knacked bushes, sort them now. Lever down the top wishbone and bolt back to top ball-joint, TIGHTEN 2 bolts as before. ALL OTHER BOLTS LEFT SLIGHTLY LOOSE AT THIS STAGE.
Refit the wheel, jack up, remove axle stands and lower to the ground. NOW TIGHTEN EVERYTHING UP WITH THE SUSPENSION LOADED UP.
Took me about 3 hours to do the front, with a big mate and a scaffold tube helping with the leverage. Second side was quicker than the first
NOTE:had a PM, you may or may not have the split collars on your lower front shocker bolts, mine did have, I have the later type CAST lower wishbones, could be that the earlier type fabricated ones don`t have.
Just checked in the manual, this IS the case, early type wishbone does NOT have the split collar.