Yes, you can easily change your United Airlines flight. If you can do so within 24 hours of booking and at least two days before departure, you’ll receive a full refund. Nonrefundable tickets can be changed for a fee, but you’ll get a travel credit. For more information, call 1-888-829-1467. Does United Airlines let you cancel within 24 hours? 24-Hour Window: The flexibility to change or cancel your flight is available only within 24 hours from the time you made the booking.