You want to find out what version of Avatax for Magento you are using.
- In Magento, go to System > Magento Connect Magento Connect Manager
- Enter your credentials and log into Magento Connect Manager
Find your AvaTax extension; often labeled OnePica_AvaTax and see the Installed column
Note: If you cannot locate your extension it may have been installed manually on the back end of your website. You will need to discuss this with you web developer if this is the case.