4.7. Control Panel> Company > General > Close Account
A company’s MME account can be deleted by an Administrative User. While MME staff can also remove an MME account from the system, this menu location makes it possible for a company to control their own MME account and delete it if they want to discontinue use of the app. This does not affect the installed package and uploaded/synced data in Salesforce. It only removes the MME account from the MME server. This cannot be undone and there is a second confirmation step to be sure the action is desired.
Click here to find a more detailed article about stopping use of Match My Email.