Contact Membership Administration to change your name. You can change your name on the reservation yourself online if you are not lead guest. If you are, contact MS via phone or chat.
You will also need to change it on MDE so reach out to them for that.
You can change your name in the eyes of Disney without changing your deed. I changed my name 5 years ago with member services and I am only now changing the deeds to reflect my current name. I was adding my daughters to my contracts so it was easy to update my name on the deeds at the same time.