Sign in at
https://billing.microsoft.com with your subscription LiveID. If you have a credit card on file and it is valid, you will be charged for renewal. However, I believe you will actually get a free 6 month extension first and will be offered Morro for free when it becomes available later this year.
To completely prevent renewal and remove OneCare, you will need to contact support to cancel your subscription before the renewal date.
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator