If you are looking to play this game, it has been remade into Final Fantasy XIV: A Realm Reborn (a much better experience). To manage your Final Fantasy XIV subscription, head over to the Mog Station. It is a website operated by Square Enix (the developers and publishers of Final Fantasy) that will allow you to renew your subscription or add game time cards, change the subscription length, update payment method, purchase expansions or cosmetics, etc.