Grasp the Bottom Housing by the left and right edges and slowly wiggle it out. There will be some resistance, but it will come. Only pull it out enough, at first, to get a peek inside at the connectors and wire routing. Do not put undue strain on the connectors or you may pull them off the logic board!

CAUTION! If you are following this guide to disassemble an earlier model iMac G4, you will encounter an entirely different situation when removing the Bottom Housing. On those models, there will be a fixed connector that will disconnect as you separate the Bottom Housing from the Upper Housing. That connector will be on your left or Airport Card side of the computer. Use extreme caution, making sure to apply your removal pressure evenly so that you don't twist the Bottom Housing open and bend the pins on the fixed connector.