Yes, just go online to change your flight and re-book at lower rate (even if it is the same flight #etc) you will get a "credit" which goes in a travel bank for a year.
Good luck!
The "year" vassar36 is referring to is one year from the original booking date, provided no travel funds were used to pay for the flight. If travel funds were used when booking this flight then the expiration date of the earliest expiring funds applies.