If you are a current customer, you can purchase again to renew your access to the software for another year. As long as you use the same email at purchase (better yet, login before purchasing!) you'll keep the same account and have access to your existing data.
Simply log in and click on the "Purchase" button at the top of the screen to get started. If you're in the application and don't see a "Purchase" button, click on Account > Account Information in the top right corner of your screen and then click on the "Renew" button.
MaxiFi customers receive a discount for renewing prior to expiration of the current subscription. There is no discount price for renewals of Maximize My Social Security.