Just finished replacing my rear rotor and pads on my 05 Subaru WRX and wanted to share some pics since I could only find the STI pics online.
1. loosen lug nuts, jack up car, put on jack stand, remove tire
2. remove two bolts holding on the caliper (spray with PB blaster and wait a couple minutes) and remove caliper, hang with wire or hold up with extra jack stand or box to not put any weight on the brake line.
3. Remove brake pads (they pull straight off)
4. remove two bolts holding the caliper bracket (spray with PB blaster and wait a couple minutes) (if you're having trouble getting these off apply more PB Blaster and wait longer) You can also apply anti-seize when putting them back in.
5. Pull the caliper bracket off.
6. Remove rotor by pulling straight off. Mine was seized on pretty good. You might get away with hitting with a hammer, I had to use two 8mm bolts and screw in allowing the rotor to be pushed off. Once it broke free, it pulled off easily.
7. Clean parts and reassemble.