Go to Services, select Manage TV. On the right you will see an option to Add/Manage Premium channels. This will take you to a screen where you will see all the included channels and the optional ones. If you have subscribed to Acorn then you will see that it is checked. Uncheck this and then select Review at top of the screen. Then will take you to a screen where you will accept the change. Once you accept the change Acorn should be gone. Be aware then when you make this change Xfinity will immediate reset your set top box (at no charge!).