OSX VERSION 5.8 I WANT UPGRADE TO LION

I WANT TO RUN PARALLELS 7 AND WINDOWS 7 ON MY MAC AIR OSX VERSION 10.5.8. THE TEST VERSION OF PARALLELS INSTALLED AND SO DID THE WINDOWS PROGRAM THAT I BOUGHT. I AM TRYING TO INSTALL THE PARALLELS PROGRAM THAT I JUST PURCHASED AND IT WON'T INSTALL. I RECEIVE THE MESSAGE THAT I NEED TO RUN THE PREUPGRADE SCRIPT FOR PARALLELS HYPERVISOR.

I CAN'T FIND SUCH AN UPGRADE.

IS THE REASON MY PARALLES WON'T INSTALL IS BECAUSE I AM USING THE OS 10.5.8?