Deltech Fitness DF2000- Standard Weight Bench - Manual (Page 9)

ADJUSTING THE WEIGHT ARMS: RAISE AND LOWER THE WEIGHT ARMS
USING THE PULL PIN. TURN THE KNOB TO LOOSEN FOR ADJUSTMENT.
MAKE SURE THE PULL PIN IS SECURE IN THE ADJUSTMENT HOLE THEN
TURN THE KNOB TO TIGHTEN BEFORE USE. (THE PULL PIN IS DESIGNED
TO FIT TIGHTLY AGAINST THE TUBE AND WILL NOT ADJUST UNLESS IT IS
LOOSENED FIRST.) THE LEG EXTENSION IS ADJUSTED THE SAME WAY.
ADJUSTMENT