Modules and Views → Projects → Manage Items → Role Assignments
You can make role assignments for a user and/or a security group while you are creating a new work item.
A role assignment is a way to grant to a user and/or a security group permission to access any individual work item in the work item heirarchy, including all of its associated data and any of a child work item.
You can clear any role assignment. Clearing a role assignment will prevent users and/or security groups from being able to edit information in any child work item; however, users and/or security groups will always be able to view data in a child work item if they have permission to view its parent.
If you are not using a role assignment, you can delete it (though it may be better to clear it).
You can modify a role assignment.
You can remove a security role assignment made to a work item. Select a work item, view its properties, and then remove the role assignment.