Lift the back vertically out of the base of the chair. Wiggle it back and forth if necessary.
Set the base on the floor upside-down. Find the pins on either side at the front of the base. They anchor the arc-shaped metal pieces in place. Use the screwdriver to unscrew the screws holding the pins in place.
Slide out the pins toward the center of the base. Lift the base front.
Remove the screws that fasten the arms to the seat and lift the seat out of the arms chassis.