Assuming this still works and Delta has not closed the loophole, here is what you need to do. Book a ticket (now) for dates beyond the current expiration date. Try and find a fare that is as close to the fare you have (Maybe a few dollars more to make sure you use the entire current ticket amount). Say February 16 to February 28. Once it is purchased, wait about 3 days (to make sure you go beyond the grace period for cancelling the tickets). Then go in and cancel the reservation. It "should" give you a new expiration date one year from the date you make this reservation. YMMV