Hi Stefans,
If you are referring to the plastic sleeves the headrest poles slide into, they are friction fit - pressed in. I imagine they would be very tough to pull back out - they are like giant panel push-clips. Not much instruction here I am afraid other than brute force. I suppose you could drill it out to loosen it up for removal - but this would take some great care.
Generally speaking, you would need to remove the seat from the car to dismantle the upper seat back if you had to push the guides from underneath.