• "I want to do a clean install of Windows8"
- have a look here: http://windows.microsoft.com/e.....-windows-8
• "the only disk that came with the laptop was a 'Product recovery disk'"
- A recovery disc is a general term for media containing a backup of the original factory condition or a favored condition of a computer as configured by an original equipment manufacturer ... these recovery discs are commonly shipped with most computers to allow the user to reformat the hard drive and reinstall the operating system and pre-loaded software as it was when it was shipped.
hope that clears up what that recovery disc is for and what you might need it for in the future. as for the upgrade, check out that link and it will break down the steps / options you can take.