Check via Magento admin:Log into your Magento Admin Backend, Scroll to the bottom of the page in the Magento Admin Footer. The version number is listed in the center of the footer
You can also use a Chrome extension
Magento version can be checked in app/Mage.php file of your Magento installation, simply search for getVersionInfo() function there:
Some stores have the release notes and you can check at the following url: http://www.domain.com/RELEASE_NOTES.txt
Find version using SSH:
- Login to server via SSH using root password, go to the directory where the Magento is installed and type the below command to find the Magento version installed.
php -r “include ‘app/Mage.php’; echo ‘Magento version is: ‘, Mage::getVersion(); ”