You use Windows AD with the Folder Redirection rules for AppData, Documents etc. for the AD users to redirect to a network or DFS share (which is useful for backups and fast logins). One user account has to be renamed.
Rename the account in „Active Directory Users and Computers“. Also change the path of the user profile, if you set one.
The part which is a little bit tricky is to move the user data files (appdata, …) to a new DFS share with the correct user name. Just renaming the folder causes the event log to show error message of folder redirection:
Event ID 502 / Folder Redirection: Failed to apply policy and redirect folder „<folder name>“ to „<path>“. Redirection options: 0x9021. Details: This file is currently not available for use on this computer.
Even though the files are available, the error appears.
Leave the original folder as is (with original name) and create a new one with the new user name, and correct permissions (e.g. full access for Admins, SYSTEM and the user, owner: user).
Log in as the user, go to the original userdata folder and set the option „make available offline“ (right click).
Look into your event log, everything should be fine now and you can delete the old userdata folder.