If you want to cancel auto renewal for your Norton 360, you can do it through your Norton Account (here is the My Norton sign in page). Once signed in, go to My Subscriptions page, and click the link that says Cancel Subscription Renewal. A window will pop up asking you to confirm your choice.
With Automatic Renewal turned off, you will still get prompted by your installed software to renew your subscription.
Here are step by step instructions with screenshots:
Manage Automatic Renewal in your Norton Account
In addition, you can delete your payment information.