I have a return award booked for HEL-BKK in PE. If AY will release U availability to my outbound flight, what would be the process to try to get an upgrade from PE to J (for outbound flight only ) if I wanted to use Avios? Would AY allow me to just pay the difference in points and the additional booking fee for AY J award? Or would I potentially need to cancel my trip and then try to rebook in U?