If you want to cancel auto renewal for your Norton 360, you can do it through your Norton Account (here is the sign in page). Once signed in, go to Automatic Renewal and Subscriptions page, and move the slider to OFF position for the product for which you want to turn Auto Renewal off. 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 including screenshots and the video: