On Windows, you can uninstall using the system “Add or Remove Software.”
On Mac OS X, you can uninstall by moving WordPress.com app from Applications to the Trash. To remove all settings you can use this WordPress.com Uninstall script for Mac.
After uninstalling the app, you can check your app data folder to completely remove any application data that isn’t removed by the Windows uninstaller or Mac uninstall script.
For Linux (Ubuntu), you can open the Ubuntu Software channel and click on the “Installed” tab at the top center and then find the WordPress.com app and click the “Remove” button.