How do I change/update my payment method?

You would log into the primary account via https://hd.islandnet.com/

Under the Account Menu select Account Details.

The Account details show your account package, usage, credits and charges and there is a button labeled Account Settings above and to the right of the Resource Usage pane.  

Clicking on this will take you into an area where you can change payment details, statement format and plan type etc.

Dont forget to go to the end of the page and Save Changes to apply.