I have a bad feeling this may not be possible, but I have a LH metal flight IAH-FRA booked under the CO code in C. The flight is O1, so it should be possible to upgrade if it were booked under LH code, but is it possible to upgrade if booked as CO code? eVouchers would be used, but miles would be possible too if they would work.

I can probably standby at the gate otherwise, but would prefer to confirm now if possible!