How long do I have to change my ticket?
The time you have depends on the fare you purchased. Check how much time you have in the Ticket's Purchase Receipt in the section “Maximum stay in destination,” which is the same amount of time you have to make changes to your ticket. In general, you have up to one year (from the purchase date) to change it, as long as you haven’t flown one of the legs.
Remember to look at your flight time. If you make changes after that time, the penalty fee could be higher or could prevent you from making changes.