Keep in mind that if you’re changing to a costlier flight, you'll be liable for any difference in airfare price. However, if you’re changing to a less costly flight, you'll not receive any kind of credit or refund for the difference in fare.
Changing to a special flight on an equivalent day? Frontier Airlines cancellation policy offers a “Same Day Confirmed” alternate flight option for a flat fee of $119. This is often offered at no additional charge for Frontier Miles Elite members, or for those that purchased the Works add-on.