A User is a person with login credentials to the Auctria event dashboard who helps organize and manage the fundraiser. They are usually fellow members of your organization, board members, or volunteers. Users can be assigned different permission levels to control what they can access and edit.
See Users for details on adding users and managing permissions.
In general, the User Identity (read: email) is not modifiable.
If you need to change the email address of a User Account you will need to Add A New User and Remove the incorrect one. Please see Adding Users and Removing Users for more details.