參考這裡（ref here )http://superuser.com/questions/130260/how-to-update-google-chrome-in-ubuntu
You must have http://dl.google.com/linux/deb/ in repo list
Now open a terminal. Type following -
sudo apt-get --only-upgrade install google-chrome-stable
This will install the current stable version of it. Now you have to kill all instances (may be hidden) of old Google Chrome.
sudo pkill -15 google-chrome
sudo pkill -15 chrome
Then start google-chrome as you start it.
