The complicated answer is that you buy (or make) a shock absorber spring compressing tool.
If I can find it, could get a pic if any interest.
Don't know what the simple answer is - a strong pair of hands, a pair of tyre levers, and a helpful octopus to hold it all while you heave ??
P.S. Don't know what happens when you have all-enclosing tin covers on the shocks, and strong springs, that must be a juggling act ? Perhaps a pair of threaded rods, and some flat bar to press on things ???