To update your subscription and add payment information, go to the Settings page and click on the Update Subscription link.
Note: This link is only visible for the account owner and billing liaisons. Learn about roles and permissions, here.
You should see a popup like the one below:
Select the plan you would like to subscribe to, and then click on the blue Next Step button.
You will see a popup like the one below:
If you are subscribing to a paid plan, you will see a field to add a card. Update the fields and submit the form.