Nope, you don't need to buy an update. Note your serial key. Save & Run 'Nero General Clean Tool', downloadable from here, to uninstall your nero. Reboot. Download from here and install Nero 6 Update
Providing you have your Nero 6 serial number, as stated you can update to latest versions of Nero 6, however if it's Nero 7 or Nero 8 you want then you will have to outlay the appropriate purchase price. Nero was offering a discount to existing licence holders but I am unsure if it is still in effect.
Thanks Guy's. You're info was just what I was looking for. I am at the latest version of 6 so I'll check into the pricing of the latest version of 8. Are there enough enhancements in 8 to make it worth my time and money to update?