Upgrading an avios booking on CX/KA
I have a booking using Avios, Booked on ba.com NRT-HKG-RGN.
NRT-HKG in Premium Economy.
HKG-RGN in Economy.
Ideally i'd fly business all the way. Business has opened up NRT-HKG. How do I best upgrade this sector? And the second sector at a later date should availability become available?
Thank you very much.