whenever i need to replace something like that, i go to the junkyard and pull one first. That way, im figureing how it comes apart on the junkyard car, not my own, in case i break something.
The power assembly is held on by two clips. The assembly will pull out just be firm. If the round plastic parts fall out put them in before inserting the assembly (make sure you place the hook on the door lock first) then push hard and the assembly will snap in.
If you need a pic email me as I haven't put up my re-build website yet. (coming soon)