If you are going to try to remove the tube from the plastic case, you should discharge it first. To do that, take a flat blade screwdriver and connect it to some part of the metal frame of the Mac with a wire. Either wrap it around the screwdriver and the frame or clamp it on somehow. Then simply wedge it under the suction cup until you touch the metal clip inside. You should only use one hand and only hold onto the plastic part of the screwdriver. The ungrounded frame itself is enough to dissipate the charge in the tube. Make sure the screwdriver makes direct contact with the metal clip.

Once this is done, you are safe to unclip the suction cup and pull the video board off the very back of the tube. You may have to use a razor to cut through the glue that holds it on. Once the glue has been cut through, pull the video board STRAIGHT off of the tube. Pulling at an angle or twisting can crack the glass which ruins the tube.

I recommend leaving the coil (yoke) on the tube and simply detaching its cables from the analog board. Once these cable(s), video board, and suction cup are removed, the tube should come right out of the Mac after you remove the 4 screws holding it in there. Remember that it is glass, so if you set it on a cement floor, it will scratch it. It's best to set it on cloth / styrofoam / carpet / etc. to prevent this.

Also note that there are also some adjustment rings on the yoke. I believe these are for geometry-type adjustments or something. It's important not to disturb the position of these rings. (They should be lightly glued in place.)