First login to OpenVPN website.
Now click on "edit profile" link located at the top of the main page.
Then click the "Additional Information" tab and edit the fields on this tab.
The following information from this tab will be displayed on the Invoice.
1) Company name
3) City and State/Province
4) Country and Zip/Postal Code
5) Tax ID or additional Information
6) Phone number
You can always display the Purchase Receipt/Invoice again at any time by displaying the License Key page and then clicking the Order Number for your purchased orders.