Removing calipers
 

How easy is it to do? My rear ones are sticking and my mate has some
on his old ZS that I can have.
What tools would I need?

To remove rear calipers you will need standard size sockets and a pair of needle nose pliers to remove the pin on the end of the hand brake cable. They are on carriers like the fronts so same principle to remove.
You will probably need to wind in the new calipers to fit them over the disc, to do this just use any "ruler" shape tool such as an old file or something.
You will then need to re connect the brake hoses and hand brake followed by bleeding them. If they use banjo bolts (cant remember) then a few new sealing washers would be a good idea.

If it goes well its quite easy. If you can't get the hoses off you may have to replace the brake pipes, which I imagine is right pain on the rears. Do you really need to replace them or can they be freed up?
Basic tools should do it, but a brake spanner would be handy.

if the brakes are sticking it's usually because the slide pins are full of crap

It's worth cleaning the new ones right up before you fit them on the car too, or the same thing will happen again

start off with good tools, dont try undoing bolts with multihex sockets ect likely just round it, just did the worst ever brakes i have ever done on my girlfriends dads s plate freelander, 4 rounded seized carrier bolts, 2 seized rounded caliper bolts, had to drill out the brake disc retaining screws because they where rounded, 3 of the caliper sliders where seized into the carriers, 2 cae out with some twisting, one sheered off, so had to drill that one out, seized caliper, safe to say if i hadnt of had the right tools then it would've had to have been relayed to the garage

Bet the air was blue Ritchy, lucky it was the GF's dad, or it would have been given back!!!

I would have thought that freeing off sticking calipers would be easier than changing for new ones. Like Ritchy experienced, the carrier bolts rarely get moved so can be an absolute swine to get off. Then there's the hassle of getting the handbrake cables out of the way without damaging them, and bleeding the new calipers afterwards.
The only things that can really stick are the sliding pins (usually easily rectified) or the piston itself, and if you can get the caliper clear of the disc then a stamp on the pedal should budge it. After that you just need to wind it in and out a couple of times, and perhaps spray some WD40 up under the piston seal.