An upgrade isn't a perk that's just for the asking --- it's available sometimes, and certainly worth inquiring about, but don't get your heart set on it and be disappointed.
Smile when you check in, ask politely, act enthusiastic, mention your anniversary, and don't act as if you expect to be entitled to a complimentary upgrade. Some people have great luck (or pixie dust) and have been automatically upgraded when they arrive. Unless a CM informs you that there's an upgrade available for xx$$ more, it's a complimentary upgrade. They have to inform you of any change in rate ---- and I can't ever recall reading anyone say they were charged more and didn't know it. If the price isn't something you care to pay, just decline the offer. No big deal and don't be embarassed for asking. Lots of people ask.
The upgrade is generally to a room with a nicer view. If you have standard view booked, you might get a water view. Rarely, it could be to a suite or concierge (which isn't available at your resort). If you already have a water view, I don't believe there's too much else to upgrade to. There ARE some 'suites' that are a bedroom plus an ajoining room, but it's much less likely to get that kind of an upgrade.
Good luck! It just might happen --- and you can certainly have a spectacular trip whether it does or it doesn't.