United publishes flight schedules up to 11 months in advance to give you as much time as possible to plan your trips. United Airlines provides multiple options for changing an existing air travel reservation, including requesting a refund, switching to a different United flight leaving in the next three hours on the same day as your original reservation or changing your reservation to an entirely different time or location. To change your flight on United, log in to an existing united account and select your itinerary. Search for and select the new flight to which you want to switch. Then select the earlier flight, if available, and indicate you want to switch to standby status. A fee applies, charged only if you successfully board the earlier flight.You can also call to change your reservations or switch to a same-day reservation.Approach a United Airlines representative at a United counter within the airport to change your reservation or move to an earlier flight.