To update your card details, head over to:
Account > Billing
On the right hand said, there is a Update your credit card here section, just click on the blue 'here'.
You should be greeted with this screen:
If you do not see any area to enter in a credit card, make sure to check the Pay all invoices or Pay minimum number of invoices buttons
If you pay the outstanding invoices (or if you have paid them all already, just hit the pay all invoices button), it will give you the option to update your credit card details online.
(note: if you would like to reduce your costs towards your fees, you can also purchase prepaid fees which include a bonus that go towards your fees).
For more information, please reach out to a member of the support team.
Other Resources: