If you are subscribed via iTunes we can't administrate your subscription for you - however, you can manage it using Apple's tools (either on your device or desktop machine). To do that use the menu to open the 'subscription' panel and then click on the 'cancel subscription' button:
which will pop you over to the iTunes store where you can cancel your current subscription (or change the billing period).
Once you've changed your subscription, you may need to close and reopen RINGR (Or logout and in again) to pick up the change to your subscription status. For more details on managing your subscription via the Appstore please see this Apple support article.
If you've cancelled your current subscription you will be presented with more options: