Passengers who wish to change their flight can do so up to 24 hours before their scheduled departure time. However, any changes made to the itinerary may be subject to a change fee, which varies depending on the type of fare purchased and the specific route. United Airlines Change Flight allows passengers to change their flights, including changing the date, time, or destination of their itinerary. Passengers can make changes to their flights through the airline's website, mobile app, or by calling the United Airlines reservations department.