All online payments are handled via PayPal. Subscriptions are active until cancelled (once you have a subscription you will see a big red "Discontinue Subscription" button on the payments page). If you discontinue at any point you will remain upgraded until the end of the current billing cycle, and if you have time remaining on an existing upgrade we will credit your new subscription with the left over time (you will never "lose" paid upgrade time).
If you'd rather use a payment method other than PayPal, contact us and we'll be happy to set something up (rates will be the same as through PayPal). We're willing to be flexible; the last thing we would want is for you to want to pay for our service and not be able to.