You can update your credit/debit card or Paypal details by logging into your Geckoboard account and doing the following:
1. In the top right corner, click your initials and from the drop-down, select ‘Account'
2. Click the 'Plans & Billing’ tab on the left side of the screen
3. Click the ‘Change Billing Details’ button
4. Click the ‘Edit payment details’ button
5. Update your details and click ‘Save'
You can also change from credit/debit card to Paypal and vice versa using the aforementioned process.
If you run into any trouble doing this, please get in touch.