If you pledged without creating an account first you must create an account.
if you created an account during your pledge:
- Login to seedandspark.com with your account information
- Click the yellow banner at the top of the page. If you cannot see that for any reason, Select Manage Account from profile menu on far right
Select Pledges on the left hand side of the screen
From there you can find the pledge you've made and update the payment details. Please double check that your browser doesn't auto-populate the expiration date, otherwise it will get declined with an error saying your security code is wrong.