Yes, upgrades once you are on board can be pricey. You are now a captive audience. The only way to move is to complain about somthing other than size, like noise, and hope they will be willing to help you out.
But, I doubt that you will care.
These are really good cabins. We've introduced some local friends to these and now that is all that they will book!
Hope it works out for you. It makes it easier to cruise in today's economy when the cabin price is so tight!