GMC Safari 2003 Owner's Manual page 62

4. Buckle the belt. Make sure the release button is
positioned so you would be able to unbuckle the
safety belt quickly if you ever had to.
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5. To tighten the belt, pull up on the shoulder belt
while you push down on the child restraint. If
you're using a forward-facing child restraint, you
may find it helpful to use your knee to push down on
the child restraint as you tighten the belt.
6. Push and pull the child restraint in different
directions to be sure it is secure.
To remove the child restraint, just unbuckle the vehicle's
safety belt and let it go back all the way. The safety
belt will move freely again and be ready to work for an
adult or larger child passenger.