If you'd like to remove individual users access to a project this is possible by clicking on:
'Share Project' > 'Manage' (top-right corner of the overlay).
You will see a list of all users that have access to the project. To remove any of them, just click on the trash icon.
Alternatively, if you click on the pencil icon beside, you can modify permissions in that project for that particular user. Click here to see how.