Removing access to a private or hidden work item
Removing a colleague from the work team and unassigning them from any tasks, emails or notes within that work item will remove their access to the work item. If they are on the client team, they will still have access to the contact.
Removing access to a private or hidden contact
Removing a colleague from the client team for the contact will remove their access to the contact and any associated work items.
When on the contact, click the details tab. Edit the client team by clicking on edit on the right and then hit the "x" to remove a member.