Delta Airlines offers several options for seat selection, both at the time of booking and before or during your flight.

1. Seat selection at the time of booking: When you book your flight, you can choose from a variety of seat options, including standard economy seats, extra legroom seats, and premium seats such as Delta Comfort+. You can select your seat using Delta's online booking platform or through a Delta agent over the phone.
2. Seat selection before your flight: You can also select your seat through Delta's Manage Reservations tool, which is available on Delta's website or mobile app. You can use this tool to change your seat or upgrade to a premium seat before your flight.
3. On-board seat selection: If you did not select your seat at the time of booking or before your flight, you can choose from any remaining seats during boarding. You can ask a Delta gate agent for help with seat selection or use the Delta mobile app to select your seat from your smartphone.

Keep in mind that Delta seat selection is subject to availability, and certain premium seats may require an additional fee. Additionally, Delta reserves the right to reassign seats for operational, safety, or security reasons, and seat assignments are not guaranteed.