Hi! I’ll be flying from Buenos Aires to London for my job. They will book me a ticket in economy, but I would like to upgrade to business. Which airline gives me better chances to get a relatively cheap upgrade in advance? And do all of them let you upgrade from the app as soon as you have the reservation code? I know Lufthansa offers you the upgrade as soon as you’ve bought the ticket (+ has bidding option). What about the rest?

Some airline options I have are: Lufthansa, Air France, KLM, Iberia, British