How do I convert the car seat to backless booster mode?

To convert to backless booster mode, loosen the harness straps, push down on the harness release lever, and remove the harness straps from the splitter plate. With the car seat in the 6th recline position, lift the red backrest locks and slide them together, then push the seat back up and lift it out of the base. Store the splitter plate and buckle strap, attach the base pad to the back of the base with elastic straps, and place the booster seat forward-facing in the vehicle's back seat. (Page 7)