Pontiac 2001 Aztek Owner's Manual page 36

Shoulder Belt Height Adjuster
Before you begin to drive, move the shoulder belt
adjuster to the height that is right for you.
1-24
To move it down, push down on the button 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 the button down 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.