How to remove a user registration from Office 365 SharePoint.
Useful for renaming a user or removing a user in order to reuse an email address.
Go to a site in your collection, Click the settings cog/Site Settings.
Under Users and Permissions, click People and Groups.
Click on any of the groups.
Go to the end of the current URL and change the GroupID to 0 (zero).
This will show you a list of all users and allow you to remove the user from the site collection from the Actions menu.
