You can go to your Paypal
History and look at the Details of the "Subscription Creation". From there, either the Buyer OR the Seller can cancel. You still get the benefit of the most recent payment for however long it was supposed to last, not that you should care.
If you're afraid you'll forget about the subscription and not have enough money available when the time comes, then by all means, go ahead and cancel today. There is no drawback to doing so.