If you no longer with to share your project with someone, you can revoke their access (if you are the owner of the project):
- Open the project
- Choose File > Share from the menu bar at the top of the screen (or click the popup menu in the window's title bar)
- Select the person whose access you want to revoke
- Click the "-" minus button.
- Click OK.
The person will no longer have access to the project.