Hey there, Sheyla! Welcome to planDisney. You've brought us a great question and I'd be happy to help get you an answer.
When you are planning a visit to Disneyland Resort, you need both a ticket and a
theme park ticket reservation to enter the parks. If you are visiting with a one-day ticket, these tickets are tiered. You are able to visit and make reservations for any date that has a tier equal to or less than your ticket. In your instance, you would be able to make a reservation for any day that is a tier 4 ticket, as well as a tier 3, tier, 2, tier 1, or tier 0. If you already have a reservation booked, you will just need to log into your Disney account and modify your current reservation to the new date. If there is not a reservation available for the new date you are wanting to visit, just keep checking. The reservation system is fluid and new reservations could open up before the date.
Be sure to take some time to stop and visit
Mickey's Toontown and the newest attraction,
Mickey & Minnie's Runaway Railway. The newly imagined space is so fun and there is lots to explore for Guests of all ages.
Sheyla, I hope you found this information helpful. If you have any other questions, be sure to stop by again and ask for our help!
Carrie