Go to the User CP (control panel), top left, in the gray header. In the left sidebar, scroll down to Miscellaneous, Paid Subscriptions. In there you will find a link to PayPal to pay $25 for a one year membership. When the membership is due to expire, you will get an e-mail a couple days ahead of time, but it doesn't hurt to check the date it expires, which you can find in the same section, and renew before it actually expires.