Can I use LATCH/UAS to install the seat if my child weighs more than 40 lbs?

No, you must not use the lower anchors (LATCH/UAS system) to attach this child restraint when restraining a child weighing more than 18 kg (40 lbs) with the internal harness. For children over 40 lbs using the internal harness, you must use vehicle belt installation only. (Page 16)