Buick 2004 Rendezvous Owner's Manual page 10

To lower the seat, push the lever down. Adjust the seat
and release the lever.
1-4
To raise the seat, pull up on
the lever located on the
front right side of the seat.
CAUTION:
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You can lose control of the vehicle if you try to
adjust a manual driver's seat while the vehicle
is moving. The sudden movement could startle
and confuse you, or make you push a pedal
when you don't want to. Adjust the driver's
seat only when the vehicle is not moving.