Cancel or change my flight date: which one costs less?

It depends on your fare, but a quick way to decide:

1. Check the change fee in your fare rules or under Manage Booking.
2. Compare it with the cancellation outcome. Cancelling a non-refundable ticket usually gives a credit or only taxes back.
3. Look at the new fare. If the price went up, a change may include the fare difference.
4. Within 24 hours of booking? For flights to or from the US, booked at least 7 days before departure, you can generally cancel for a full refund and rebook.

Compare both numbers before you decide. This page on how to cancel flight ticket online shows where to check the details.