You'll want to release the parking brake then back off on the adjuster. The latter is next to the parking brake lever inside the car and can be accessed by removing the boot around the p.b. lever (pry it to the side, towards the driver's seat, and unclip it from center console.)

You can tell if there is a star adjuster because if there is one, there will be a hole of about 1/2 inch diameter in the rotor among the wheel studs. If you have this hole get a bright flashlight and look for the star wheel by rotating the brake rotor and hub. On my car the hole was near but not at 12 O'clock when the wheel could be seen. You can inch the wheel along with a screwdriver having a flat 1/4 inch blade, inserted thru the hole. Do this with the rotor in place. I think you will need to push upward, pull out the screwdriver, and push upward again a couple of times. If you are going the wrong way the rotor will become tight as if the parking brake was set. Try to remember roughly how far you turned the star wheel. If you can get back to the same point then you won't have to mess with the parking brake cables (assuming they are adjusted ok) or do anything else to get the parking brake to work at the end of the job.

The new models may be different... In the 850/70 cars, there is a trap door under the center arm rest. Pull it up and the Ebrake adjustment is there. I use a torx#40 to loosen it up as much as possible with the brake handle down.

When I pulled off my V70 rotors, I still had to turn the star wheels. Your car has them also and can only be seen through the lug hole with a small flashlight. Lety is loosey.

Before you put the rear rotors back on, make sure that the two metal "L" brackets are at 90 degrees. Those brackets keep the shoes from touching the side of the rotor. I bent mine trying to get the rotor off, wound up driving around with a scrunch,scrunch noise for about 2K miles until I fix it.

Klaus
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The 164 has a new home, all I am left with are 2 turbos :)

Usually giving it a couple of yanks or rocking side to side will get it off. Make sure that the parking brake is released (easy to forget). If it won't move at all, squirt some pblaster through the lug nut holes to disolve any rust between the rotor and the wheel and turn the wheel a few times so the solvent will cover the inside of the rotor well.
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1998 Volvo S70