Since you have already parted with your N9 why are you still interested to update to PR1.1? But since you ask it is actually very simple. Just download NSU and install it on your PC. NSU will update itself to the latest version, then connect your N9 to your PC in sync mode and it will look for the updated firmware and do the rest. Be patient because it is a 1.1GB download. After completion NSU may say "update failed". Just ignore it, reboot your phone and enjoy PR1.1. But I still wonder why you are asking.