If you have moved house/office or for some other reason you need to update your billing address you will find this option in your Accounts area.
Click on your name top right and then Manage your account
At the moment your billing address is tied to your card so you will need to click the Change Card button.
Add in your current card details and the new address, click Update Details to finish and you are all done.
From now on all your future invoices will have the new address on.