For monthly subscriptions, yes. You need to cancel your subscription by going into PayPal and cancel the recurring subscription.
For yearly subscriptions, no. When your license expires, your credit card will not automatically be charged. You will need to go into MyPhotoApp and click on the license tab and renew your subscription manually.
About 2 weeks before your license expires, you will start to get reminder emails that your subscription is about to expire.
If you don't want to renew your subscription, you don't need to do anything and your subscription will automatically cancel on the license expiration date.