How do I convert the Evenflo 4-in-1 from harness mode to high-back booster mode?

To convert to high-back booster mode: (1) Loosen harness straps by pushing the harness release button and extend them completely, then unfasten the chest clip and buckle; (2) Remove the crotch buckle from its slot and store it in the storage space at the rear of the seat base; (3) Lift the headrest pad, disconnect hook-and-loop connectors, and push shoulder straps behind the headrest; (4) Pull harness straps, chest clip, and buckle tongues through the forward-facing belt guides and snap the chest clip together behind the seat; (5) Replace the headrest pad and adjust to upright position. (Pages 56-57)