Can I use SkyMiles or Medallion upgrades for Premium Select or Comfort+?

It depends on your status, fare and availability:

1. Medallion members may be eligible for complimentary or discounted upgrades, but not on every fare or flight.
2. Miles upgrades may be offered on some fares, and the price changes by route.
3. Check Manage Trip for the upgrade options shown for your booking.
4. Availability matters. Premium Select cabins are small and can sell out.

Compare the cash price with the miles price before deciding. More on the Delta Comfort+ vs Premium Select difference is here.