Hi, Suzel!
You can definitely upgrade your Annual Pass to the Premium Annual Pass that includes admission to the two Water Parks and DisneyQuest. When you upgrade, you will only be required to pay the difference in price between those two passes. You can view the most current Annual Pass pricing information
here.
The most important thing to keep in mind is that your current Annual Pass will still have the same expiration date. The price will not be pro-rated when you upgrade. So, in other words, if your current Annual Pass expires in a few months from now and you upgrade to a Premium Annual Pass, your Premium Annual Pass will still expire in a few months. I'd say it would be worth it for me if I had at least 6 months to go before my expiration date.
Our kids have the Premium Annual Passes in our family because they love to go to the Water Parks as much as possible. They are also old enough to hang out at
DisneyQuest Indoor Interactive Theme Park while my husband and I have a date night at Downtown Disney. This makes the price well worth it for our family!
Thanks so much for stopping by the Moms Panel with your question and I sure hope this helps. Please don't hesitate to write back if you have any additional questions that we can help with.
Have a Pixie Dusted day!
~Jackie