When an easyJet aircraft is changed from A321 to A320, or A320 to A319, or A319 (156) to A319 (150), passengers are informed (using the email address on their booking) that the aircraft operating their flight has changed (or it’s configuration has changed). If the passenger can’t be bothered to read the instructions in that email (i.e. check your allocated seat for possible changes, and download their revised Boarding Pass), I’ve no sympathy. It’s not rocket science for most people, unless they’re on Mars with no Space X connection.