CITROEN DS3 Owner's Handbook Manual page 80

Additional adjustments
Head restraint height adjustment
To raise the head restraint, pull it upwards.
To remove the head restraint, press the
lug A and pull the head restraint upwards.
To put the head restraint back in place,
engage the head restraint stems in the
openings keeping them in line with the seat
back.
To lower the head restraint, press the lug A
and the head restraint at the same time.
The head restraint is fitted with a frame
with notches which prevents it from
lowering; this is a safety device in case
of impact.
The adjustment is correct when the
upper edge of the head restraint is
level with the top of the head.
Never drive with the head restraints
removed; they must be in place and
adjusted correctly.