Users within the websites can be managed by the central administrator or the site administrator.

1. Go to Management.
2. Then click on the Users button under the users section.
3. Now you can see all users in your website(s). Check the box next to the user you want to remove. This can be one or more users.
4. Scroll back up and then click on the field next to action, select Delete selected users.
5. Then press the Execute button. 
6. A screen will appear where you can double-check who you are deleting. Everything checked? Then click Yes, I'm sure.

The users are now removed and no longer have access to the website(s).

You can safely remove users without losing the content they have uploaded