Contact your travel agent and if there are cabins 'free' to upgrade to they will change the booking and all you do is pay the extra as listed in the brochure or on the website. OV has been sailing quite full so any upgrades they may give (if you are lucky?) will just be another deck. Bear in mind that higher decks equal more movement and if those cabins are the 'unchosen' then they are probably not so well positioned. If offered free upgrade - check it out first to see if the cabin is in the right place for your needs.