Hi Lillie!
Thank you for bringing your question to the Disney Parks Moms Panel. I know when I visit
Walt Disney World Resort, I try and squeeze in as much park time as humanly possible, so I understand wanting to potentially add a day to your ticket!
You can
upgrade your ticket as long as it is within 14 days of its first use and there are still valid admissions left. Since your current tickets were from a limited time promotion, I wanted to double check with a Cast Member that the same ticket upgrade rules apply and they told me they did! Based on the price of the 4 Park Magic Ticket that ran as a promotion earlier this year, you may find that it is cheaper to pay the difference and upgrade your entire ticket to a
5 day ticket, rather than pay for a single day admission ticket. You can upgrade your ticket at any theme park ticket window, Guest Relations location or the Lobby Concierge at your Walt Disney World Resort hotel.
Please let us know if you have any other questions before your upcoming trip!
-Lindsey ºOº