If I change my subscription price will existing subcribers pay the new price or the old price?
Subscription Pricing
When it comes time for them to renew they will be charged the new price. If it is a price increase, the App Store will issue an alert asking if they agree to the increased price.
Thank you, If they don't agree will the subscription be canceled?
If they don't agree to the price increase the subscription will not be renewed and the subscription will end when the existing paid period of subscription ends.