Can I change between yearly and quarterly subscriptions?
In order to switch subscriptions, you will need to cancel your current subscription and resubscribe with the new billing plan of your choice when the current subscription expired. For example, if you are on a quarterly plan and switch to yearly, you have to cancel the subscription before the next quarterly payment and select yearly when the quarter has finished. Please visit https://support.google.com/googleplay/answer/7018481?ref_topic=1689236 for how to manage your subscriptions.