How do I install the Tranzitions as a high back booster seat?

To install as a high back booster: (1) Remove the harness system and back support, (2) Unhook tether and lay it in seat, (3) Place seat forward-facing in vehicle back seat, (4) If using LATCH, extend and attach strap to lower anchors and tether, (5) Thread vehicle shoulder belt through seat belt guide on headrest, (6) Verify seat does not move more than 1 inch (2.5 cm). The child must be secured with vehicle lap/shoulder seat belt. (Page 44-51)