866-227-1888 is the fastest way I’ve found to check real upgrade availability. On my last Carnival cruise, I booked an interior cabin because it was cheap, but a week before sailing I got the itch to upgrade. The website showed “limited availability,” but nothing specific. When I called, the agent actually walked me through open rooms deck by deck. I ended up grabbing a mid-ship balcony for way less than I expected. They also explained the difference between a paid upgrade and a “bid,” which helped me decide. The whole call took maybe 10 minutes. If you’re flexible with decks or views, you can usually snag a solid deal.