What you are asking here... is in the wrong section of the forums.
But removing a CRT may and will be very dangerous. The capacitors powering a CRT Screen uses voltage beyond three digits. (1000v+)
Touch one of those, and you will probably have serious injuries.
You cannot just "Disconnect" a CRT from that IMac, but you'll have to cut the cables. And by cutting those cables, you take off the insulation, and you can get shocked.
Overall its a bad idea, and most people would go against doing that. But if you accept the risks, you can try wearing a insulated glove or a very thick cotton glove.
Cut the cables attaching the CRT To the case and take it out by paying attention to not touch any of those big capacitors.
-Hope it helps!