Hi Helen,
Thanks so much for visiting us at the Disney Parks Moms Panel!
I'm happy to let you know that if you decide you're having such an amazing time at the most magical place on earth and you wish to
upgrade your tickets, you
are able to do that, and you'll only need to pay the current difference between the new tickets and the tickets you currently have. You won't need to buy a single day ticket!
As long as it's still within 14 days of your tickets' first use and you still have at least one day remaining on your tickets, simply take them to a theme park ticket window,
Guest Relations location, or even just to your Disney Resort hotel
Lobby Concierge desk, and a Cast Member will be able to help you with upgrading your tickets. You'll be on your way to even more fun before you know it!
Please let us know if you have any other questions as you're planning your trip, Helen, as we're always happy to help. I hope you have a truly magical vacation!
Missy