Hello,
Click on the "Upgrade" link in this page https://www.stardock.com/products/windowblinds/, refer screenshot below. Click on that green "Upgrade" button, enter your email account that linked to your WB6/WB7 when the popup box appear. It will show you if you eligible for discount or not.

Thanks
Basj,
Stardock Community Assistant.

I am just telling what I know, I am not the one who can check your account eligibility for discount. So, what result do you get when you enter your email address? Not eligible? If so, Please raise support ticket using the link below, use "Ask a question" option. Include all information details. Remember to record down the ticket number for future reference if needed. Do not raise multiple ticket, that will make your ticket back to the end of the line. Send once and wait. Ticket will be answer by the order they send in.

https://stardock.atlassian.net/servicedesk/customer/portal/4/group/13

Thanks
Basj,
Stardock Community Assistant