Originally Posted by
49penguins
Finally got a straight answer out of calling Delta. Award seats booked by Korean Air in economy are booked into a non-upgradeable category and Delta cannot rebook it. (I'm not a Medallion member.)
Any route where DL sells C+ as a separate fare class you will need to book the award as a C+ award. There is no "upgrade" path for non-Medallions other than to cancel your existing award and rebook as a new C+ award.