You can view the all the changes on git.hazzardweb.com by logging in with your Envato account.
admin.login(only if you use the default authentication system)
Because of the major changes from the previous version, you can't just update the script. Also the old database tables are not compatible with the new ones.
Howerver, you can use the Upgrade Tool and transfer your comments from the old table to the new one. Make sure you backup everything and test it locally first.
To begin you will need 2 databases. One for the new comments and another one for the old comments. First make sure you have installed the script.
upgrade folder, then copy the files from the Upgrade Tool inside that folder. Next edit
upgrade/database.php and configure your old database connection.
Now open in your browser
upgrade/comments.php to transfer your comments.
Only if you used the old authentication driver and want to transfer the users to the new table, open in your browser
Because the new authentication driver uses another password hashing algorithm you'll have to change it so it matches to the old one. Edit
comments/src/Auth/Hasher.php and uncomment the commented lines.