Greetings Jayson,
Welcome to the Disney Parks Moms Panel. I hope you are having a Dapper day!
I'm thrilled to infinity & beyond that you have an upcoming visit to The Happiest Place on Earth soon. You are sure to make memories that will last a lifetime! I'm glad you have purchased a Theme Park Hopper Ticket as well, it's so fun to be able to "hop" over to the other park during the day.
You can upgrade your 3-Day Park Hopper Ticket to a 4-Day Park Hopper Ticket; more Disney days mean more pixie dusted days! Just stop by any Theme Park Main Entrance Ticket Booth to upgrade the 3-Day Park Hopper Ticket, at that point, you will pay the difference between the 3-Day Park Hopper Ticket and the 4-Day Park Hopper Ticket. You will need to upgrade your Ticket before the end of the 3rd Day Use, any days you have used will be deducted from your 4-Day Park Hopper Ticket.
I hope this helps and that you have a pixie dusted time on your next visit. If you have any more questions, please visit me here and let me know how I can help you plan your magical vacation.
Happy Disney Park Hopping!
~ Lynette