I figured out how Delta seat upgrades work after booking a Main Cabin ticket for a long weekend trip. At first, I just selected a standard seat, but a few days later I noticed upgrade offers popping up in my reservation—Comfort+ and even First Class for certain legs. On one trip, I used miles to upgrade, and on another, I waited and cleared a complimentary upgrade closer to departure. When my return plans changed and I didn’t want to lose the upgrade, I called 8 8 8-2 1 7-3 3 2 4, which turned out to be the best way to instantly book, cancel, or modify flights without messing anything up.
