Most of the time chrome will update on the background when we open and relaunch chrome browser. But if for some reason the chrome browser remains up for long time, Likely will have pending updates.
Follow this steps to Update Google Chrome
1. Open chrome
2. At top right, click on three vertical dots 
3. Click on Update Google Chrome
(Note: You can't find this button, if you're on the latest version)
4. Click Relaunch
The browser saves the opened tabs and windows and reopens automatically when it restarts. If you'd not like to restart right away, click Not now. The update will be applied next time when the browser restarts.