You can change the credit card on file with your account if you have Admin rights.
Since Gliffy Online does not store your credit card information online, you will need to input all of the new credit card information and click "Purchase" to change the payment information.
From Account Settings, click into Payment Info.
On the next screen select either a Gliffy Personal, Team or Enterprise account.
Choose the number of users you want and the monthly or annual option for payment.
Complete the entire billing information portion.
*If you are unable to get to the screen above, use the link here.*
You will charged for the plan you select in full on your new card as soon as you click "Purchase" and prorated back any unused portion of your current plan. You can view your charges and refunds/prorations under Account History.