Both the chrome and the native (OSX, Windows, and Linux) apps can be force-upgraded. To find the current version of your app, head to the Settings (top-right corner of the app) > About.
Chrome apps generally update automatically. To force an update, check the details here
Native apps (OSX, Windows, Linux) will show you a popup when an update is available. This can also be accessed through the Settings > Update tab. Documentation for the same is present here.