The Preview user appears if you have clicked on 'Enter student preview' on a module
- and when you exited the preview you didn't select to delete the preview user.
If you go into the modules listed for the preview user , enter student preview then when you exit student preview make sure you select
'Delete the preview user and all data (Recommended)'
Once you have done this on any modules that your Previewuser account is attached to it will disappear