Hiya Anjalina! Welcome to planDisney. You've brought us a great question!
To answer the first part of your question, you actually don't have to change the name on your ticket if you don't care. If it's a standard theme park ticket, anyone can use that ticket as long as it's unused. This is because the ticket doesn't get assigned to someone until it is scanned at the park entrance for the first time. A Cast Member will take your picture and this is what will assign the ticket to a person. If you do want to get the name changed, the person who purchased the ticket will just need to
call in or chat in the
Disneyland app and request the name change which can be done anytime before the ticket is used for the first time.
Technically, you can make a
theme park ticket reservation on the same day you visit. However, I would not suggest that. Theme park ticket reservations for a day can and do book up. I recommend making the theme park ticket reservation as soon as you can. If you decide to go on a different day you can go in and cancel that reservation and then make a new reservation.
Anjalina, I hope this helps you as you start to make your plans to visit Disneyland Resort. We hope to see you real soon!
Carrie