They should move by themselves, once the seat bottom has been lifted. Spray some stuff (WD40, TriFlow) on all of the joints and get it all lubed up, then fiddle until it comes lose. Try pushing the black spring metal lever up and down while you wiggle it. I used to have to do this to free mine until I lubed it and it worked all by itself (I thought I broke it at first by lubing it but now know it is supposed to work that way).
1986 300E Anthracite + ECodes + MB Mileage Award