On first selecting ‘Edit user settings’ from the More... page, you are shown the list of users; click on one of these to change the settings for that user. You should then be presented which a page showing the current security settings which you can change (user preferences are not shown here because users can change those themselves).
The settings are:
The changes will be applied only when you click Update.
Please see the Users documentation for more details on what a user name is, etc.
Note that topics set to be local topics will never be visible to remote users.