You may have a User you wish to delete from the 4th Office. Rather than deleting a User the 4th Office allows you to retain their conversations and documents but block them from your community.
You may also have an internal User who you wish to change to an external, or vice versa.
In all cases, the first step is to navigate to the User's Profile view. You can do this by clicking on their name wherever you see it in the 4th Office, or by searching for them.
Make sure you are in the Profile view. Then click Settings (on the right).
From here you can select whether the User is external or internal.
You can also select whether the User should be blocked
Once a user is blocked you will still be able to see all their discussions and items within the 4th Office, but they will not be able to access your community.
To learn more about User types, please view this article