Hi all, another followup.

I have a ticket bought on delta, from JFK to Europe, the flight is DL operated but for some reason the flight number is AF codeshare flight number. I'm booked straight into Premium Select, but I don't see the usual option to upgrade to Delta one (with cash) if I'd like. Does the flight have to be a DL flight number? I know United allows us to call in and have codeshare flight numbers reissued in the native airline flight number. Not sure if something similar is needed for Delta? Is there a certain minimum fare class PY has to be to be upgrade eligible? Thanks for any details in advance. Im new to the Delta world.