How do I know what version of Office Chat I have?

From your Windows desktop app:
  1. Click on the “gear” icon, next to the search bar, in the upper-right corner of your screen.
  2. On the preferences dialog box which opens, click on the “About” tab.
  3. Office chat “Version” is mentioned on this tab.

The Windows desktop client automatically checks and notifies you when a newer version is available to upgrade.