Hi Abby! Thanks for dropping by planDisney with your question.
I see you'll be arriving in just a few days. I think it's a wonderful idea to upgrade your
Park Hopper admission ticket, so you can enjoy more time in the parks. The magical news is that you can absolutely do this! To upgrade your 2-day Park Hopper to a 3-day Park Hopper, you'll simply go to one of the Ticket Booths at the Main Entrance, where a helpful Cast Member can assist you. Just know that this upgrade is subject to availability and you will have to pay the difference. I would also check the
Theme Park Reservation Availability Calendar before your arrival to ensure that the third day is available.
With your extra day, there will be more time to explore
Disney100 Celebration at Disneyland Resort, which is already underway. I have heard fantastic things about
Wondrous Journeys in Disneyland Park and
World of Color - ONE in Disney California Adventure Park from my planDisney friends, who have been lucky enough to already see these nighttime shows. Get ready to experience all the emotions! I'd definitely try to ride
Mickey & Minnie's Runaway Railway in Mickey's Toontown at Disneyland Park too. The queue even looks adorable.
Have the best trip.
Elizabeth