Customers can request a subscription cancellation from their Profile in the Community. Staff users will need to process the cancellation to complete the request. There is currently no workflow in place to alert staff users when a customer has elected to cancel a membership. You will need to develop that workflow for your org on your own.
Navigate to to the subscription record in question. You can either locate the subscription from a Contact's Membership related list or from the Memberships tab.
Click Related to access related lists.
Locate the Terms related list and click the current term. The term record will open.
The Cancellation Requested field is located under Details. It will be checked if the customer has requested their subscription be cancelled.
If the field is checked, navigate back to the related subscription record.
Click Edit to open the Edit window.
Select Cancelled as the Status.
Type the Cancellation Reason.
You now have the option to refund payments related to the subscription. Read up on refunds here. You will still be able to find the original Sales Order on the term record for the subscription in the Sales Order field located under Source should you need it.