The actions described here can only be performed by the clinic manager.
To add or update your payment information, from the top bar, click My clinic > General info.
If you are subscribing for the first time, click on Become a Member and enter your payment information as instructed.
If you are updating your payment information, click Update. 
Then enter your credit card information and click Update.
Your invoice will automatically be updated when practitioners are added to your clinic or when their access is revoked or regranted.