Hey there Julee,
Welcome to planDisney and thanks so much for your question! It looks like your trip to the Happiest Place on Earth is coming up in just a few short weeks! Have you started counting down the days, yet?
The 1-day theme park tickets follow a
tier system (Tiers 0-6) depending on the day. The higher tier tickets cost a bit more but have a wider date range available that you can use them on. From my experience, the lower tier days tend to have lighter crowds but usually also fall on days with shorter park hours and more attractions down for refurbishment - depending on the season.
For the date that you submitted with your question, December 16, you would need a Tier 6 ticket to enter one of the parks. Since you already have a ticket, you're correct that you can upgrade from your current ticket to the Tier 6 ticket and just pay the difference in price!
I'm not sure what your current ticket tier level is or what you paid for it, but you should be able to get an idea of the total cost for a Tier 6 ticket if you visit the
theme park ticket purchase page as if you were buying new tickets and it will show you a calendar of dates with ticket prices when going to reserve your ticket date - though don't purchase a new ticket quite yet!
You'll actually upgrade your existing ticket by
calling a Cast Member at the Tickets line. The Cast Member will be able to see the specifics of your current ticket and walk you through the upgrade process to get you the ticket you need for the date of your visit.
Once that ticket has been upgraded and you've made your
theme park reservation for the date you want to visit, then you're ready to make new magical memories at the Disneyland Resort!
Thanks again for your question, Julee. I hope you have a fantastic time!
Have a Magical Day,
Greg