Hello -- new to the FlyingBlue program so I'm hoping someone can help me understand how upgrades work.

I've been a long-time top-tier elite with Air Canada, and just recently jumped ship to FlyingBlue. On Air Canada, we would receive "eUpgrade credits", dependent upon your Aeroplan status and mileage flown and spend. Whenever you'd reach a certain threshold in a calendar year, you'd 'earn' these eUpgrade Credits that could then be used for upgrading on a future flight (either to premium economy or business, and dependent upon the class of service on the ticket you're wishing to upgrade on). You'd also be gifted these credits at the beginning of the calendar year based on your status. Note that these eUpgrade credits are different than the miles that you accrue with Aeroplan. On VERY rare occasions, at the gate you could receive a "complimentary" upgrade. I think in my 6+ years of flying Air Canada, this maybe happened twice.

So how do upgrades work on FlyingBlue? I'm looking through the FlyingBlue website and not finding anything obvious as to how upgrades work.

thanks in advance!