The subscription will begin immediately, and will be automatically renewed unless it is terminated. The License can terminated until the renewal date, and the termination will take effect at the end of the then current subscription period. The payments of the current subscription period will not be refunded.
To terminate (cancel) your subscrption, you need your subscription ID. You can find it on the My Payments page under Manage your subscription:

If you wish to terminate the subscription, please contact us by filling in this form.