Files and projects can be shared with collaborators or with Members of your Studio.
Once you're done collaborating with a user, you can remove them by clicking the 'Share' icon next to the corresponding Project in your Home View,
Finding the collaborator you wish to remove in the 'Shared With' section in the Sharing Dialog,
And then clicking the 'X' icon next to the collaborator's name and email address. Remember to click 'Confirm' to fully revoke the shared Project.