Help CenteriOS
All subscriptions and purchases are handled by Apple and connected to your iTunes account. So, what you need to do first is cancel your subscription and wait until that runs out. Then you can change the subscription plan.
Tap here to manage and cancel the subscription
Android
All subscriptions and purchases are handled by Google Play. So, what you need to do first is cancel your subscription and wait until that runs out - then you can change the subscription plan.