Upgrading seats on Delta can be done through SkyMiles miles, complimentary upgrades for Medallion members, or paid upgrades available at booking, check-in, or the gate. Options include moving to Comfort Plus, First Class, or Delta One on long-haul routes. Complimentary upgrades are prioritized by loyalty status and fare class, while all passengers can view available paid options online. International upgrades often require certificates or higher mileage redemptions. Since upgrade policies and prices vary by route, to check eligibility or confirm costs for your specific trip, call Delta Airlines at 877-297-0699.