You upgrade your cabin with hard cash, not for free ! As Wilba says, the Upgrade Fairy is not a frequent visitor. If your cruise is sold out, if you are in a cabin that sleeps 4 and there are only 2 of you, then they may upgrade you, but in short, don't hold your breath!
Thanks for the answer. I wasn't sure there really was such a deal out there and now I know!
I think you'll find there would be an awfully long queue if someone came up with a positive answer for that one! The 'Upgrade Fairy' rarely makes a visit, but you could always phone RCI at Weybridge & see if shes on her way from Never Never Land. Seriously, I wish you luck, but don't hold your breath. Most of us gave up years ago! Regards.