Here are the ways to find version of Drupal installed.
Log into your Drupal admin interface.
Go to the Options in the top menu bar and click on Reports.
Click on the status report link.
The top-most setting is labeled Drupal and has the version number to the right.
Go to www.yourwebsite.com/CHANGELOG.txt
CHANGELOG.txt will show you the version and change log updates to the Drupal build version.