Go to HP website which is appropriate for your country.
This is for United Kingdom: http://www8.hp.com/uk/en/support-drivers.html
For other countries, click the link at bottom-left of the above page before proceeding further.
Note: there are dozens of models in the Pavilion G6 range. You will need to know the full model number of yours.
This should be printed on a sticker underneath it.