I have just replaced the bellows on my Alko 3004 hitch as the old one had split.
Pretty straightforward job, only two bolts to undo.
Made a drift from an old bolt to knock out the rear bolt and stop the damper from popping out.

1 Undo front bolt and remove
2 Undo rear bolt and remove nut
3 Using the drift tap out the bolt and leave the drift in its place
4 Pull the hitch forward to remove
5 Pull off old bellows and replace with new
6 Slide the hitch back on
7 Insert front bolt and screw nut on loosely
8 Tap rear bolt in, pushing the drift out
9 Tighten up both bolts and torque to 86 Nm

I also took the opportunity to grease both the nipples on the drawbar.

I replaced the bolts, so removed the old front one first and cut it down to make the drift.

I should have carried out a better search before posting as Aaron has a much better explanation with pictures!
I did discover two wheel chocks clipped to the floor underneath when working on the hitch. Never knew they were there!