On a W123 there is really nothing to it, so I would guess a W124 would be about the same.
You just put the car on ramps, or jack stands. This is very important as it will collapse when an hydraulic line is opened.
All you do is remove hydraulic connections at the accumulators (it won't leak much at all from the lines during this), unbolt accumulator from bottom of car, install new accumulator, attach lines.
Add fluid to correct level in tank, start car, system will self bleed, then fill to correct level.
If doing a full replacement of fluid, there is a bleed nipple on the SLS valve in back, like a brake bleeding screw. Put a hose on it and run it into a 2 liter coke bottle or similar, crack screw, let fluid bleed, close, fill, repeat, etc.....
You may not get every last drop, but you will certainly replace the bulk of the fluid that way.
Did you also get a new filter?

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John