It is in PayPal.
You need to log into PayPal and open any transaction related to your PC subscription, at the top is a link to the main subscription account. You can find a "Cancel Subscription" button at the bottom of the page.
I've been told there is a subscription manager page in PayPal too, you can cancel your subscription there as well.
If this doesn't work for you, just shoot me a PM and we'll take care of it for you. (i'll need your PayPal email address and approx date you started you PC supporter's subscription)