At the moment, you can't change your current payment method.
If you purchased your license via Xsolla, your default payment method will be the same you used on your first transaction.
In order to modify your payment method, you will have to contact Xsolla on https://help.xsolla.com/#form and request them to modify it for you.
On the other hand, if you purchased your license via Paddle, you have a selected payment method since your first purchase, and it will be your default payment method.
If you want to modify your payment method, you will have to contact Paddle via help@paddle.com or assist@paddle.com.
If you purchase a Lifetime license it will be a one-time payment, therefore there will be no more payments.