Originally Posted by
FT Lurker
You cannot upgrade a YN ticket with cash+miles, but there is a Plan B:
You beat me to it,
FT Lurker!
But he's right. You need to call CO, book the SaverPass BF reward, but have the agent seat you in Economy. You'll then be put on the waitlist for a BF seat. See the 'Plan B' post for more info!