After you have logged in, please click on 'my details' at the top right. Here you'll find 'My Invoices'. You can click on the invoice that you wish to pay. This is only possible via the desktop computer/laptop, not via the app.
When you have clicked on pay, you will find the page where you can change the address.
Note: Changing your delivery address is only for the delivery of your purchased lots. Your address as registered in your BVA account remains unchanged. Changing your address in your account can easily be done via 'my details' at the top right in your account.