I belive you also posted your query in the "General" blog section, but I have also included my response here:
To release the Finisher, open the door on the finisher; Look to your right and find a spring loaded white plastic latch. Gently push rearward and the two white "hook" latches will release the Finisher from the Document Centre Copier.
Alternatively, If the Finisher door does not open, gently push the Finisher as much as it will move away from the Copier (about 1/4") and use a long flat head screwdriver to push the white plastic latch rearward. You do not need much force, and, of course, the copier should be unpluged from the power source AND the finisher's two cords should also be disconnected.