well crap, i just spent 10 minutes writing a reply, and the system lost it. trying again...

removing and installing the door with all its brackets in place should be possible in theory, but would definately require two people. changing out brackets one at a time isn't a bad job for a man alone.

for the bottom unit, there is a little plate "stop thing" at the rear of the track that you'll need to remove. and with it gone, its easy to remove the bracket, just slide it back and out. thats with it removed from the door to be easy, but should be possible when attached with a helper.
i believe its screws are a philips #4, so you might be able to get by with a 3 if thats all you have, but a 4 is right. assuming you don't have that monster, hit up harbor freight, they have a set of screwdriver tipped sockets in big sizes like this for pretty cheap.

as for supporting the door, i've been known to use a floor jack with a block of wood on top, or a ratchet strap hanging from the rafters above.

once you have the door in place, you'll likely need to adjust the roller on the top track. with the 3 screws that hold hte bracket to the door loosened, move it until the height is right, tighten it down, and slowly close the door, looking carefully for how the front latch aligns. you can move the roller in and out against its bracket to get it lined up right.

from there, you just get to play with the rear latch post until you find the sweet spot for that.

as for the lock, remove the inside door panel (if present), find the lock, pull off the retaining clip, disconnect the one linkage arm, and swap locks with your original door. they're pretty easy.