Due to inappropriate knowledge of online flight booking, have you made a reservation on the basic economy by default? Further realized incorrect reservations on seeking the notification regarding reservations. It’s not too late to edit the reservation and appeal for a seat change by abiding by Delta Airlines Seat Upgrade. Although, you might need to pay the difference amount as per the seat upgrade service of Delta Airlines. 

To leverage the seat upgrade with Delta Airlines Reservations, you can use miles or cash as per the class.

Source: https://uolsocial.socioon.com/read-blog/7615_delta-seat-upgrade-possibility-to-switch-to-the-higher-class.html