how Check magento verison

The copyright notice in /skin/frontend/default/default/css/styles.css is already a good indicator.

Magento 1.9.1.1         Copyright (c) 2006-2016 X.commerce, Inc. (http://www.magento.com)

Magento 1.9         Copyright (c) 2006-2014 X.commerce, Inc. (http://www.magento.com)

Magento 1.8         Copyright (c) 2013 Magento Inc. (http://www.magentocommerce.com)

Magento 1.7         Copyright (c) 2012 Magento Inc. (http://www.magentocommerce.com)

Magento 1.6         Copyright (c) 2011 Magento Inc. (http://www.magentocommerce.com)

Magento 1.4.1-1.5   Copyright (c) 2010 Magento Inc. (http://www.magentocommerce.com)

Magento 1.4.0       Copyright (c) 2009 Irubin Consulting Inc. DBA Varien (http://www.varien.com)

Magento 1.0-1.3     Copyright (c) 2008 Irubin Consulting Inc. DBA Varien (http://www.varien.com)