As of 2026, you generally cannot use a Delta eCredit directly to purchase a "post-purchase" upgrade (such as clicking "Upgrade with Miles or Money" in the app after you have already booked). Delta's systems typically treat eCredits as a form of payment for the base fare of a new ticket. To use an eCredit for a higher class of service, the most effective method is to apply the credit at the time of initial booking to buy a First Class or Delta Comfort+ ticket outright. If you have already booked an Economy ticket and want to use an eCredit to move up, you usually have to "Change Flight," select the same flight, choose the higher cabin, and then apply the eCredit toward the fare difference during the checkout process. Note that eCredits cannot be used for ancillary fees like baggage or in-flight Wi-Fi; they are strictly for air transportation and government-imposed taxes.