xuser [-U <user_key>] [-c <os_user>\<domain>] clear
In order to delete all XUSER entries assigned to your operating system user, do not specify any options.
Caution
XUSER is not a tool for users. It only manages XUSER entries for these users in the XUSER program. Deleting an XUSER entry does not mean that the corresponding user is also deleted. To delete users, use Database Studio or Database Manager CLI.