Managing your users is extremely important. If you are planning on having a student or outside associate help design/construct sites, you must first add them as a user for that particular site. Any person in the site’s list of users will be able to edit/change the site at any time. Depending on the role you gave the person will dictate how much authorization they have.
Removing a user is as simple as clicking remove next to their profile.
Find out more about properly adding new users.