All new & existing subscriptions paid by the end of the month will ship the second week of the following month. If your subscription is due on the 11th of the month your subscription will auto-renew for the next period unless you have cancelled.
Prepaid subscriptions allow you to pay for several renewals and shipments up front. This means you pay less on a per month basis than if your subscription renewed monthly. Since the entire prepay term is paid for up front, you will pay the aggregated shipping cost of all the shipments. You will not be charged again for any renewal or shipments throughout the course of the prepaid period. Prepaid subscriptions renew at the end of the prepay term for the original term length. This means that if you initially subscribed for a 3 month prepay of a monthly subscription, it would renew for an additional 3 months at the end of the subscription term. Lastly, it's important to note that if you change your product or term for your subscription, the changes won't take effect until the prepaid subscription term ends. This is because that prepay and its shipments were already paid and accounted for.
You are able to cancel any active subscription using your account. Keep in mind though, this will not issue a refund but simply stop the subscription from renewing. To do so, Log In and click Active Subscriptions. Then click Manage Subscriptions and, finally, Cancel Subscription.