Hey there Mary,
Welcome to planDisney and thank you so much for your question! You can now officially say you have a trip to the Disneyland Resort scheduled for "next month" - how exciting! Have you started counting down the days, yet?
It sounds like you're looking to upgrade your existing
2-day tickets to be 3-day tickets instead. I just had to do this very same thing for a trip I took at the end of last year! The good news is that this is pretty common and is possible for most standard theme park tickets.
To check your tickets' eligibility and actually make the upgrade for the additional day, you'll need to
call a Cast Member at the Tickets line. They'll be able to review the details of your specific situation and let you know what your options are.
In the meantime, as you continue to plan your trip, make sure to check out the
Disney Parks Blog! It has some really helpful articles about all the fun extras happening around the Happiest Place on Earth. Also, you'll be visiting during
Pixar Fest, which includes special character experiences, themed food and drink options, and unique merchandise. You're going to have such a great time!
Thanks again for your question, Mary! I hope you have a wonderful time at the Disneyland Resort.
Have a Magical Day,
Greg