Wayne you need to log into your router. Normally this is done by typing http://192.168.0.1 into your explorer address bar. You will need the username and password to log into your router if you know them. If you dont you may need to do a factory reset, factory is normally "admin" for username and "password" for password for netgear router login if you have not set them iirc. You will then need to find the firmware upgrade page to load the file you have downloaded then run the update from there.
Visiting Netgears website will tell you everything you need to know.