Hummer H2 2010 Owner's Manual page 41

Pull the head restraint up to raise it. To lower the head
restraint, press the button, located on the top of the
seatback, and push the restraint down.
Push down on the head restraint after the button is
released to make sure that it is locked in place.
The head restraints are not designed to be removed.
The rear seat has head rests that can be adjusted up
and down.
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