In short: Lift the car, remove the rear wheels. Adjust til the wheel is locked, loosen the adjuster until the wheel moves freely. But not too much!
Good link: http://photo.platonoff.com/Auto/20050709.Saab_9-5_rear_brakes_fixed/
The adjuster is reached with a flat screwdriver through a hole in the brake disc. It's hard to see, but theese pictures of how it looks with the disc removed can help.
Brake pads go out...
...and in. This is on left side (driver side, swedish car), on the right side it's the other way around.
Inspection holes in position for adjustment:
Looking through the hole: