DB Update Scripts when upgrading from older version's

Hello,  
   When we are migrating from 3.6 or older to 4.4 or higher version how to run the upgrade scripts. In the 4.4 assets we don't have the upgrade script and the db is upgraded automatically after first time use but how to upgrade the older one to 4.4.

https://www.nopcommerce.com/en/boards/topic/94381/i-want-to-upgrade-nop-version-39-to-45#296197

Get each upgrade script you need from here:
https://github.com/nopSolutions/nopCommerce/tree/develop/upgradescripts

Thanks so much. Each DB upgrade from 3.9 - 4.0 - 4.1- 4.2-4.3 says we need to take back up of the data settings and installed plugins json files. can we take back up at 3.9 and copy the same at 4.4 once db is upgraded all the way to 4.4 or do we need to check each version successful upgrade. Please guide.

File backups are needed as part of upgrade, but are not really related to the DB upgrade scripts.  You can just backup those files once.  Note 3rd party plugins may have their own upgrade instructions, so contact the vendor.  (You will definitely need to download/install their plugin to match for your new nopCommerce version.)