Changing Subscription Preferences
You will be taken to a page with 3 package options - you simply need to choose the free package on the left, and your subscription will be automatically downgraded at the end of your current billing cycle, and you won't be re-billed. You can still use any remaining downloads you have in your account before the downgrade happens.
To delete your account entirely, in your Account Settings, choose the "Delete account" link at the bottom of the page. Please be aware that if you choose to delete your account, any remaining downloads for your current billing cycle will be lost.