If a user shouldn't have access to your Elements platform, you can update deactivate their user. To do this, you will go to Setup > Users > Users. You can also use the Quick Find box in Setup to search for Users.

Then, you will choose the User you would like to deactivate and click Edit to the left of their name. Finally, on the right column, uncheck the Active box, then Save.

Things to note: 

1. Deactivated users will no longer be able to access Elements with that username.
2. You cannot delete a User.
3. This does allow the license to be used for someone else's User.