There are dozens of different models in the G6 range. Just posting "Pavilion G6" is not enough information. Look underneath for the complete model number.
Only certain models in the Pavilion G6 range can run Windows 8.
Go here and enter the full model number: http://www8.hp.com/uk/en/support-drivers.html
If the UK website is not appropriate for your location, click the link at bottom-left of page.