Using itunes restore you iphone. Select the shift key on your keyboard and click the restore button in itunes. And itunes will ask you to select the firmware. Select the firmware you just downloaded and it will do the rest.
Once iphone reboots it will be updated but locked, to unlock and jail brake read on.
Run quickpwn it will ask for the firmware, point to it and then it will ask you what installer you want to use and also give you the unlock option.