Hey there Thuy,
Welcome to planDisney and thanks so much for stopping by with your question!
This question is a bit tricky as it depends on what type of reservation that you're talking about - but I love tricky questions! I'll do my best to outline all the possibilities and options you have here.
First, if you're talking about changing the name on a
theme park ticket and its corresponding
theme park reservation then you're in luck. The name you assign to a ticket when you purchase it is more used more so to help you keep tickets organized amongst your party members but the name on a standard ticket does not lock in who is allowed to use it. Instead, when a Guest scans their ticket for the first time to enter a park, the Cast Member at the entry gate will take a picture that will be attributed to the ticket they use to enter. It's then that the ticket is "locked in" and must be used by the same Guest for its duration.
Second, if you're thinking of a
hotel reservation of some kind, it's also likely that you won't need to worry about changing names here either, but I would recommend reaching out directly to the hotel to confirm.
Third, if you're talking about a special event, tour, or some other alternative I didn't directly mention, then I would recommend
reaching out directly to a Cast Member at the Guest Information line! I'm convinced they know everything there is to know about all things Disney and they have been immensely helpful to me when working on trip details similar to this in the past.
I hope that helps, Thuy! Thanks again for stopping by with your question and I hope you have a lovely time on your visit to the Happiest Place on Earth.
Have a Magical Day,
Greg