U.S, May 1 -- As the summer season approaches, many people are excitedly awaiting their upcoming vacations while searching for ways to save money on unnecessary expenses, such as upgrades for plane seats. However, a few additional inches of legroom and a more comfortable seat can significantly improve your flight - and it's even better if it's free of charge.

To increase the chances of receiving a seat upgrade, experts in frequent flyer programs have revealed their top strategies for obtaining a complimentary flight upgrade and demystified some of the secrets behind the seat allocation system, helping travelers maximize the value of their plane tickets.

Free upgrades on flights are not common, but they do exist. Not all flights are comp...