You can change your payment method by logging into your My Account area: https://account.iljmail.com/my-account
Then you click on “Payment Methods” over on the left menu.
You will see something similar to this:
Click the Add payment method button to add a new card.
Add your new card in that screen and click "Add payment method" at the bottom.
Then you should see both your payment methods listed. Click the "Make Default" button by the new one and then the "Delete" button by the old one.
Then you are done!
Note: The only way to delete a payment method is to add a new one first.