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 button to open the Share Menu.
Find the collaborator you wish to remove in the list and click the … icon next to their name, then 'Remove from project.'
Note: If you have paid studio collaborators included in your subscription, removing them from specific projects will not remove them from your plan. If you wish to remove a paid collaborator from your subscription please consult the article on Adding & Removing a Paid Studio Collaborator.