If you've subscribed to Windscribe using Paypal, you will keep being billed for the subscription with the same credit card/method you selected during the initial checkout process. You can change this dynamically without having to cancel your subscription.
If you want to change which method of payment Paypal charges for your Windscribe subscription, follow these steps:
After this, your new payment method will be billed without the subscription being cancelled.
If you've paid for the subscription directly with a credit card on the Windscribe website, you can change which credit card is getting billed using the steps in this article.
Unfortunately at this time there is no way to swap your subscription between Paypal and a direct credit card payment or vice versa. For that you would need to cancel and resubscribe using the new method.