Updates are available if the wrench icon on the browser toolbar shows a little arrow  update notification. To apply the update, just follow the steps below.

  1. Click the wrench icon on the browser toolbar.
  2. Select Update Google Chrome.
  3. In the confirmation dialog that appears, click Restart. The browser saves your opened tabs and windows and reopens them automatically when it restarts. If you’d prefer not to restart right away, click Not now. The next time you restart your browser, the update will automatically be applied.

More information for Mac and Linux users

  • Mac users: You can also set up automatic browser updates for all users of your computer if Google Chrome is installed in your Applications folder. Go to the “About Google Chrome” dialog and look for the Set Up Automatic Updates for All Users button. If it’s available, click the button and authenticate to set up automatic updates.
  • Linux users: Use your package manager to update Google Chrome

Source :
http://www.google.com/support/chrome/bin/answer.py?hl=en&answer=95414