To find out the version of Magento installed on your system via the command line, you can use the following command in the Magento root directory:
php bin/magento --version
or
grep -A6 'static function getVersionInfo' app/Mage.php
From a browser you may try to reach the following page:
https://yourwebsite/magento_version
This will display the version number of Magento installed on your system.