Originally Posted by jackiedada

Is that even possible? I think if you are able to upgrade with miles to J before hand, then you should be able to upgrade on-board to F. I am not sure if the Purser can upgrade you directly from Y to F by deducting double the miles?

I think the best option would be to go and speak to the Purser just as you enter the a/c, even before you've made it to your seat - ask the SFS or any of the crew. If you are on the A380, then choose a seat in the first mini-cabin as that is where the Pursur sits, so you can just ask him/ her as soon as he/she returns back.