Due to the regulation of the Apple App Store and Google Play, when you cancel the subscription, you’ll be able to keep the function of the subscription until the end of the billing cycle. You will NOT receive a refund for your unused time.
If you choose a more expensive plan compared to your current ones, you’ll be refunded for the unused time for the current plan and be charged for the more expensive plan immediately.
If you choose a cheaper plan compared to your current ones, the change of billing will take effect starting from the next billing cycle.