This is where the magic happens :) Managing subscriptions. In the menu jus click the "Subscriptions" item and you will be redirected to the overview.
You have several things here that are very important for your download manager. The basic things are visible like the name of your customer, the product name but more imprtatnt when it was created and stops. Every subscriptions is getting an unique download ID which is giving ability to check updaters by the web. (Joomla Update System)
Further you see the toolbar buttons which might be useful. When clicking in the Customer Oververview at the geen "Add Subscriptions" button you will be redirected to the "New" screen of this part in the component.
The subscription information is clear and gives all information you need about this subscriptions. It gives information about the subsctiption, the related payment and the status of the subscriptions. Also private notes can be added to a subscription.
When cancelling the subscription, you might want to notify the customer, so when changing the state of the subscription to Cancellation/De-Activation an automated email will be delivered at the client.