It's a bit of a pain with water in it but still worth it.
Shut off the pump
Then unhook it from the nozzle that goes back into the display.
(Might have to cut the zip tie, you can get another one and secure it after the fact).
pull the tubing and the powerhead to the top
take the tubing off of the stock powerhead.
Put the tubing on the new MaxiJet
Lower it back down
attatch the top of the tubing back to the nozzle at the top of the chamber.
That's it.
I have a Maxijet 1200 and I love it. If you have any heat issues you may want to look into a MaxiJet 900. With my Maxijet and stock DX lighting I have never had the temp go above 81.