Hey Jess, Just did this last week, The ball-joint doesn't always come out nicely. You will need a ball joint separator The clamp type : http://www.amazon.com/OTC-6297-Ball-.../dp/B0015PN010
What I would do once you have the car in the air.
1) Get a block of wood Put this ontop of the upper arm and then jack the lower arm up until the block of wood is pushed up into the wheel arch/ strut tower. and the weigh of the car is on top of the wood. Be careful where you locate the wooden block as the weight of the car will be on it.
2) Get the ball joint separator and locate it into the joint (using a mallet).
(the above steps should ensure that there is plenty of pressure on the joint so it cannot rotate, The first time I did this, I had had a spinning ball joint, that had to be cut off so am now extra careful).
3) Remove the lower prong on the ball joint separator this is done by removing the clip.
4) You can now get a socket onto the balljoint and it should come off easily, once the nut is off you should now take pressure off the lower arm and just let it drop.
5) Now you can get the other two bolts off, note these are Male torx - (e18 if I remember correctly), so a spanner could be out of the question depending on what you have. If you have enough access you should now be able to swap the upper arm out.
I didn't have the right spanner etorx and didn't fancy using my multi-point ring spanners, so and had to use sockets, in this case you will need to remove the upper strut sometimes this is all you need to get access, depending on socket size etc, a 3/8 rathcet should have enough room, 1/2 ratchets are too big for the job. You may also need to remove the strut assembly but this should not be necessary and is usually more pain than its worth, you can leave the droplink attached if you remove the lower strut assembly.
Ive done the job twice with the above method and it worked perfectly, If doing it again I would get some Etorx spanners, preferably ratchet ones if your budget allows.
Also get some pure silicone grease to put on the rubber bush this should stop the rubber drying out. then copper grease the bolt too so it doesn't seize. and the job should be done. It sounds complicated but its not. Dead simple just take your time and everything should be fine.
ask if you have any more questions.