The software does not upgrade automatically, the user has to accept the upgrade. Usually, when it detects there are new versions available, you may get messages asking you to upgrade, if you accept, it will install it, so in case you get the message, you need to decline to avoid that problem. In any case, I do not know what is the exact version that is compatible with your license but you can check out this link to find it: http://www.oldversiondownload.com/
If you cannot find the correct version, you will have to contact the support team: https://www.nch.com.au/support/index.html
In case you want to upgrade, NCH offers a license upgrade discount by entering your current registration code at http://www.nch.com.au/upgrade/