usually you can just remove the chassis without having to take out the monitor.
couple of screws or small bolts and the tray the chassis sits in will come right out.
If you insist on removing the monitor (cramped, inaccessible, awkward etc) undo all the cables/wires and loosen off the nuts or bolts holding in the monitor. a 19 should be able to be removed by one person (I do 27's by myself, but I'm pretty strong though)
you don't want to remove just the tube, you want the whole frame and everything.