Yes, you can upgrade an economy ticket on Delta, but your options depend on the fare class you purchased. If you booked a standard Main Cabin or Comfort+ ticket, you can often purchase an upgrade to First Class, Premium Select, or Delta One (on international routes) using either cash or SkyMiles via the "My Trips" section of the Delta app or website. Prices for these upgrades fluctuate based on demand and are often available until check-in. However, if you purchased a Basic Economy ticket (the lowest, most restrictive fare), you are generally ineligible for any upgrades—paid or complimentary—regardless of your Medallion status. For frequent flyers with Medallion status, complimentary upgrades to Comfort+ and First Class are available on domestic flights, typically clearing between 24 hours and 5 days before departure, provided there is open seat inventory.