Renaming a Domino (Notes) user is not complex but there are several steps to the process.

Only a Domino administrator can complete the process and needs the Domino certifier ID files and password.

See this video, Registering and managing Domino users, starting at time index 2.00 to learn how to rename a user. The video renames a user's first name but you can fill in the new first, surname and short names as required.