In Blackbaud Sphere, your organization can create Gala events and allow people to register. In this situation, you are looking to change the registration type a participant selected when registering.
This is not part of the functionality for Gala events. You can change the registration type in regular Thon events if the registration was an offline transaction, or if the registration type you are selecting is the same price as the one the registrant selected. However, Gala events do not support this. You will need to reverse the registration and re-enter it.