Window Blinds 6

Hello, I have previously purchased Window Blinds 6 and have gotten a new computer since then. I see now I am unable to download 6 (that I can see). Could someone please help me out. I have my serial code for 6 but I am unsure where to place it to retrieve my download. I have place my email and the serial into the firel and it asks me to pay another 10$ for 7. I do not wish to do this.