Receive seat notifications
“There are apps and websites available, such as ExpertFlyer, which sends you notifications when a better seat becomes available on a flight.
“When it’s time to check in and a more spacious seat is available, it wouldn’t hurt to ask staff at the desk if you can move to this seat, as they can agree.”
If passengers are polite to the check-in staff, they are more likely to agree to requests.
British tourists can always see if a better seat is available when they check in and ask to transfer.