Hello there Suzanne,
Welcome back to planDisney! We're so glad to have you back with another great question.
I was especially happy to answer your question because I had a similar situation happen for one of my family trips to the Happiest Place on Earth. We realized two days was not going to be quite enough to fit in all of the magical experiences we were planning on, and when I realized how cost-effective it is to move from a
2-day to 3-day ticket - it was a no brainer!
The way that you'll want to do this is by
calling a Cast Member at the Tickets line. You can let them know that you want to upgrade your tickets to add an additional day. Just keep in mind that it will need to be equal or greater value than the tickets that you're upgrading from.
From there, you can confirm all the details on the
My Plans hub on the Disneyland Resort website. This is also a great place to see all of your reservations in one place - theme park, dining, hotel, and enchanting extras. It also has a really great daily breakdown of each of those reservations on the page as well.
More Disneyland Resort is never a bad thing in my book, Suzanne! Thanks again for your question and enjoy your visit to the parks!
Have a Magical Day,
Greg