Normally updates happen in the background when you close and reopen your computer's browser. But if you haven't closed your browser in a while, you might see a pending update:
To update Google Chrome:
The browser saves your opened tabs and windows and reopens them automatically when it restarts. Your Incognito windows won't reopen when Chrome restarts. If you'd prefer not to restart right away, click Not now. The next time you restart your browser, the update will be applied.
For Android:
Chrome should automatically update based upon your Play Store settings. You can check if there's a new version available:
For iPhone and iPad:
Chrome should automatically update based upon your Apple App Store settings. You can check if there's a new version available: