Upgrade DXB-IAD on CO codeshare
 

I am UA GS. Have full C ticket from DXB to IAD at end of June. Ticket issued on CO but metal is UA and UA MP# is in the record. Process for upgrading seems pretty vague on UA website. Is there a sure way of doing it? In advance?

Good luck. For the UDUs you'd have to be on UA code or ask at the airport. For SWUs (which is what you'll be using, right?) I also think that you're supposed to be on the UA code. But the easiest way to confirm that is to call in and ask the agent to apply one of your SWUs to the trip and see what they say.

This is a UA question.

If you are booked on a codeshare you can only request an upgrade at check-in. At that time you can use a valid UA instrument like a SWU. You cannot do a *A upgrade on any codeshare flight. If you want to request an upgrade in advance, do not book codeshares.