Originally Posted by
Gajan
I am sure others will correct me if I am wrong, but there needs to be availability in "O" to upgrade to WBC.
If you see availability at the regular WBC level, you should be able to upgrade using miles.
Upgrading from B/M/U should cost 25K miles from Europe to North-America.
Correct. Search for your flight as an award flight on the FB engine. If your specific flight displays at normal level (green?), O is available and you can call to upgrade.
Note that there is often no availability until some days bedore departure.