You cannot move up your flight earlier in the day for no charge,even on the same day. It is still a flight change and you will be charged the change fee plus any differfence in fare. If your flight on the outbound was $100 and the earlier flight you want is $200, you will be charged the $100 difference and the change fee (depending on the airline $50 - $150) per person. NO exceptions, the same as changing for a different month. However, if you arrive at the airport early, you can go standby and they may not charge you if there's room. They still may though, depends who's working.