Originally Posted by
saaveraward
Can I purchase Y now and then pay the mileage difference to upgrade if the flight becomes available with no change fee?
You will have to pay a fee unless you are GGL or above.
The standard change fee is £35. If you have paid less than that for taxes, fees and charges for your economy award ticket (for example, if you have paid only the RFS fee of £17.50), you could simply make a new booking in Club and cancel the economy booking, forfeiting the amount of cash you have paid but with no liability to pay anything more for cancellation. If you have paid more than £35 for TFC, then it doesn't really matter whether you cancel and rebook, or simply change the existing booking.