similar question please.
Several months ago we booked S fare on HKG-BKK-HKG flights but now it could make all sense to fly at least one segment in Y or H or B to qualify for current 1W promo (12,000 miles for 2 1W segments= we need just 1 segment on Cx as we will have 1 segment on BA later).
Could you please advise where and how to upgrage (fare or class

) in the most economical way?