The system does not allow you to delete users, however, you can deactivate them in order to prevent them from being able to log back into the system.
Select the 'Settings' tab on the left-hand side menu.
The 'Active' column indicates the users activity status.
If a user is active, a green 'Yes' will show in the active column.
To de-activate a user, slide the button from 'Yes' to 'No'.
A grey 'No' button shows that the user is deactivated.