Google Chrome does a good job of updating your extensions automatically, but it checks for updates on its own schedule - around every two hours or if you relaunch Chrome. If you know that a new version of an extension is out but Chrome hasn't updated it yet, here's how to do it manually
Chrome does, in fact, have an "Update Extensions" button built-in, but it's a little hidden. To manually update your add-ons, just head to chrome://extensions in your address bar and click the Developer Mode button on the right side of the header. From there, you should see the "Update Extensions Now" button pop right up. Why it's hidden away as a developer feature we're not sure, but if your favorite extension updates and Chrome hasn't caught up, that's where you'll force Chrome to pay attention.