Log into your Gameflip account and visit the Subscriptions page at Wallet/Subscriptions.
If you still have an active subscription, locate the orange button "Stop" and press it. Your subscription will be stopped and will not be renewed by the end of the current billing cycle.
If you decide to renew your subscription, simply press the "Renew" button. Renewals done before the expiration of the current billing cycle will not incur you additional charges during this billing cycle and the status of your benefits and used sales will remain the same.