The current system has two ways of becoming a premium member; the Silver Supporter (3 months) subscription and the Gold Supporter (annual) subscription. Full details for the two membership options can be found under your Payment Subscriptions area of your User CP.
It was at one time but we upgraded the service to a quarterly subscription period.
You can check out the full summary of benefits for both Silver and Gold subscriptions here: Paid Subscriptions
Also note that there is currently a temporary offer on whereby any Silver Supporter subscriptions will automatically be upgraded to Gold Supporter status at no extra cost.