Hello Tommy,
The easier way to upgrade will be to upgrade your database from 3.1 to 3.8 (following our instructions at our
documentation) and then replacing your old nopCommerce 3.1 with nopCommerce 3.8.
After that you will need to upload the Nop Traction Theme (that you`ve previously downloaded) in the nopCommerce 3.8 folder. You will need to copy the InstalledPlugins.txt and Settings.txt from App_Data of nopCommerce 3.1 to the App_Data folder of nopCommerce 3.8.
You can find more information on how to upload a theme in our
documentation.
After you have correctly uploaded the theme you will need to start your nopCommerce. Once your store starts you will need to install the Nop Traction Plugin from Administration -> Plugins -> Local Plugins.
Your last step will be changing the theme to Traction from Administration -> Settings -> General Settings.