When logged in as administrator, from the User list section in your system you are able to manage your users. You can add a new user or edit the details of an already existing one, view reports about a user or log in the system as this particular user. More over you can archive a user. This archive functionality is actually a safe delete action (1).
When you click on the corresponding icon to delete a user you will get a pop up like the following:
As described in the message of this pop up, this user you are trying to delete, will not be permanently deleted, but moved to the archive (2) where it later be restored.
To access the archive, logged in as administrator, go to your dashboard and click on the archive section (3).
Over there you will be able to see all the users you have archived (not permanently deleted).
You have the option to permanently delete these users (4) or delete some of them individually or restore them (5). Restoring user will remove them from the archived users list, and you will be able to view them in the Users list.
The same process applies also for Courses and Lessons.