First, be wary of the two big capacitors. One is the large "beer-can"-shaped component against the inside wall of the enclosure, and the other is the smaller, silver oval-shaped can right next to it. These can hold electrical charge, and could hurt you. You'll want make sure that they're discharged.
Once you unplug the unit, wait a few minutes for the caps to discharge on their own. Then, get a piece of insulated wire, or pliers with insulated handles, and short out the two terminals on the top of the cap. It may make a good spark, which is why you're doing it! Better to spark through the wire than through you :)
There's a third cap on the pcb (big silver unit with a wire coming out either end), you should probably discharge this one, too.
The white connector up top will be easy. Generally you just grab all the cables together and pull it out. There may be a latching mechanism holding things together that's not visible in the photo.
At the bottom of PCB (going by picture orientation), look at the black and brown wires that are connected to the board. The are using "quick disconnects", which can get to be fairly tight. Grab the connector (not the wire), and rock it back and forth (the long way) as you pull on it. Needle-nosed pliers might help.
Those wires have wire nuts on them too, but I would leave them alone. Once you are finished, give each wire coming from the wire nuts a firm tug, to make sure they haven't loosened up.
Oh, and I recommend marking the wires before you disconnect them. You can make small tags on the wires using masking tape.
Should be pretty straight-forward. Good luck!