I did mine out in the wilds of Macedonia with nothing more than a Leatherman and a rock. I should really post up the video of me doing it. It's quite simple. You pull out the retaining clip that holds the pin in place. knock out the pin... using aforementioned rock on the end of the leatherman and the pads just drop out.
The reverse is true for replacing the new ones. The only thing you have to do is open the brake fluid reservoir and soak up the excess when you put the new pads in. This is because the new pads will push the fluid back up the tube and displace the fluid in the reservoir.
I'm no mechanic and did it myself for the first time with very few tools in a dusty environment.
Remember not to touch the brake lever once you've got the pads out, otherwise it is a bugger forcing the pistons back to fit the pads.
Also bear in mind that the new pads will be thicker than the pads you are removing - leading to a tight fit on the brake disc when you fit the new pads.
Regarding non-BMW pads, I'm sure someone has posted their thoughts on the merits of fitting them on here. Try the FAQ sticky at the top of the 800 section Forum page.