We booked a guaranteed inside cabin in the second last category (deck 3 or 4) and were upgrade to a cabin on deck 9.
Another time we also booked an inside guaranteed cabin and got an outside cabin.
Normally you get the information about your cabin number with getting the documents. But I got a reservation number and checked the cruiselines website and saw my cabin number yet listed.
But I know from many other people, that they never have been upgraded with a guarantee cabin.
Good luck, Marita