How to register TWO TurboTax Basic cds on one computer

I have 8 simple returns to file. Since TurboTax Basic only allow 4 returns I purchased TWO TurboTax Basic CDs. I used up the first and tried to install the 2nd but it only asks to "re-install or remove". There is no questions asked to enter the new "installation key" to register the 2nd CD therefore I am still stuck with the one original CD and can't do my other 4 returns. How to I install the 2nd Cd?