Air New Zealand Air Points - Moving up to an earlier flight.

I've made reservations on an Air New Zealand flight from LAX to SYD via AKL. I noticed that Air New Zealand has two flights out of LAX, both on 747s. One at 9pm, the other at 1030pm. I'm currently booked on the latter.

In checking seat availability, I noticed the 9pm flight appears less full. If I get to the airport early, can I move up to the earlier flight? If so, at what cost?

Depends on the fare. If fully flexible economy (booking class Y) or business then no charge, subject to availability.

Otherwise there may be a change fee (the fare rules will specify the change fee) AND fare difference (if no availability in the original booking class you need to buy up to a higher booking class). This could be waived in some circumstances (eg if your flight is oversold).