To save you a long read the solution is:
For existing customers your will need to go to the license upgrade page here:
http://render.otoy.com/account/upgrade_license.php
If you purchased your standalone upgrade soon after it was released (with the free plugin upgrade deal) then it should tell you that you have a voucher at the bottom of the upgrade page. Just tick your license and click proceed, it should automatically use the voucher, upgrade your license and not ask for payment.
I will edit this post when the upgrade product is available.
EDIT: The license upgrade is now available (2014/09/16 23:35:00 GMT)
Thanks
Chris.