Web Dashboard Billing
If you subscribed to Planoly via the Web Dashboard Billing Page, to cancel your plan, please go to your Billing Page and in the BILLING box, click on Cancel.
iTunes Subscriptions In-App Subscription
If your Planoly subscription was made via Apple's In-App Subscription, you will need to cancel your subscription through Apple.
Since you subscribed on the app, the subscription is handled entirely by Apple. Please visit your iTunes manage subscriptions page to cancel. Here is a direct link: iTunes Manage Subscriptions
View this guide here for more information regarding cancelling an iTunes Subscription: iTunes | Cancel In-App Subscription
You will be on your current plan until the end of the billing cycle, which will not renew at the end. Once your billing cycle is over, you can downgrade to the Free plan on the Planoly web dashboard as well.