How do I change the email address on my invoice?

You can change all your billing details, here (including email address, credit card, and billing address):

https://www.2checkout.com/va/sales/customer/change_billing_method?sale_id=

You will need your active order number, that you can find your opensolr billing area , your last used card details OR the zip code used on the last purchase, in your case, in order to idenfity and modify your billing details.