GMC 1996 Suburban Owner's Manual page 50

To move the height adjuster down, push in at the word
PRESS and move the height adjuster to the desired
position.
You can
move the adjuster up just by pushing up
on the shoulder belt guide. After you move the adjuster to
where you want it,
try
to move it down without pushing in
to make sure it has locked into position.
Adjust the height so that the shoulder portion of the belt is
centered on your shoulder. The belt should be away from
your face and neck, but not falling off your shoulder.
2-Door Utility and Suburban
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