Google releases updates regularly. Although your Chromebook will usually update automatically, this guide will show you how to update your Chromebook manually.
Step 1: Click the Status Menu in the bottom right corner
Step 2: Open Settings
Step 3: Select About Chrome OS
Step 4: Select Check For Updates
You will now either get a message that says "Your Chromebook is up to date" or it will say "Updating", if it says updating wait until it finishes Once done the button will change to restart. After restarting your chromebook the update will be complete.