How do you cancel a subscription before it’s over?

I have subscribed to a membership for an app that lasts until July 2018. I would like to unsubscribe from the app fully- not just unsubscribe from the App Store. Is there any way of getting rid of it completely? because I really want to change stores but can’t due to on going subscriptions. Or does anyone have a way of making a second Apple ID on iOS 11?