Removal of Administrators access

Hello, all.
By default all folders (including Team) and dashboards get Administrators access, that I have not found as yet, can be removed.
we have a large number of users who can access SCOM but we definitely want to limit access to Dashboard

Can someone point me /direct to process to manage folders and dashboards without Administrative access and group access and ONLY Named users for more granular view.

Thank you,
George