Originally Posted by ag51

I had a non-flexible ticket, but once I had the email advising me that the flight had been cancelled and went into MMB, there was a message at the top of the screen - I clicked through and it was very easy to change either all or some of the legs of my trip. This was only available after the notification, though - the flight had been showing as cancelled for a few hours before that, and I couldn't change it at that stage.