Please see here for the detailed steps in the subscription FAQ:
Howtoforge offers two pyment options, Paypal and RBS Worldpay. The subscription has to be cancelled in the account that you have at one of these two payment providers.
If you used paypal to do the payment, then you must have a paypal account as paypal does not offer subscriptions without an account. If you dont find your paypal login details in the emails that ou received from paypal after you started the subscription, then please contact us by using the contact form here at howtoforge and we will cancel your subscription at paypal for you.