first make sure the pinball machine is switched off and unplugged from the power point

then get a screwdriver and attach some wire around the metal shaft of the screwdriver, attach the other end of the wire to the metal frame on the monitor chassis, make sure you strip the wire so that you are using the wire and the not the insulation for attaching

and finally push the screwdriver under the rubber suction cup on the tube and also remove the suction cup at the same time using the screwdriver (there are 2 metal prongs under the suction cup which have an L shape, you need to push the prongs one at a time so the hook pops out of the hole), you will hear some arcing when doing this, also it's advisable to discharge again before moving the tube

one last tip, when discharging the tube keep one hand in your pocket and make sure you hold the screwdriver from the plastic/rubber handle, this way you won't accidentally zap yourself

Hope this helps & is not too confusing