To check your version of Ubuntu, open a Terminal window. You can use the app icon or launch it using the keyboard shortcut Ctrl + Alt + T.
In the Terminal window, enter the following line:
lsb_release -a command
Press Enter or Return. Your Ubuntu version number will be listed on the Description line.
If you're using a version more recent than 16.04, the following command will also provide your version number in Terminal:
Users who make use of the GNOME desktop environment can find the current version listed under Settings. Choose the Details tab to confirm the exact version number.