Upgrading from Delta Comfort+ to First Class can be accomplished through several methods, depending on your SkyMiles status and the type of ticket you purchased. The most common way is via the Delta Fly App or the "My Trips" section on the Delta website; after booking, you will often see a specific "Upgrade" button that allows you to pay for the move using either cash or SkyMiles. If you are a Medallion member, you are eligible for Complimentary Upgrades, which are processed in order of status (Diamond, Platinum, Gold, then Silver) starting several days before departure down to the day of the flight. Another strategy is to monitor the seat map; as the flight date approaches, Delta often lowers the "buy-up" price to fill the premium cabin. If you are at the airport, you can ask a gate agent about "Day of Departure" upgrades, which are sometimes offered at a fixed price if seats are still available. It is important to note that if you booked a "Basic Economy" ticket, you are generally excluded from all upgrade options regardless of your status or willingness to pay, making it essential to book at least a "Main Cabin" fare if you hope to sit in First Class.