If you'd like to cancel, downgrade, upgrade, or modify your COIN subscription plan in any way, you may do so using the Account page of the COIN website.
Please visit this page and make sure you're logged into your COIN account:
IMPORTANT: Cancellation of an active subscription will take effect at the beginning of your next billing cycle.
Log Into your COIN Account, and Click "Cancel Subscription"
Confirm that you would like to cancel your subscription.
Cancel your Subscription
Here's some more resources you may find useful: