This article explains how to unlink/remove card details that are saved under your account.
Unfortunately, the card details can't be removed if your subscription is active as the card is attached to the active subscription.
To delete your card details from your account, the only option is to cancel the subscription first and then remove the card details.
You don't have to worry. Even if you cancel the subscription, you will still have the same access as a paid user till the next renewal date.