Go to a subscriber's Subscriptions and choose either Terminate or Cancel.
The customer support team would like to be able to add a note with each termination/cancellation reason. This is very important to the team, so they can track and act on selected reasons.
The revamped Customer Service admin that shipped in v1.49 includes free text note for terminate and cancellation. In an upcoming release, we'll allow for client-configurable reason codes.