To change your payment details, please follow the below steps:
Please login to your account here.
Once you log in, go to Profile section and then, click on "Membership & Payment ->"Manage Payment".
Then, click on "Payment Methods"-> Edit Payment Method.
Enter your new payment details and click on "Update".
Note: Paypal is not available in some countries, if you don't see the option under Payment Methods, then, it is not possible to switch to PayPal from Card.
Please email firstname.lastname@example.org if you face any issue.