Whoa slow down.
First is v6.4.1 is very old and may not support modern server software versions.
For example you will need php 5.3 up to possibly php5.6 max
Newer versions will work on php7.x

Try this test script.
https://www.ubbwiki.com/archive/view/58/ubb-threads-system-requirements-test-20200304.html

Second for your site what you need to do is start over , You can't just merge different versions..
Copy your backup files to a blank folder.
Then import the backup database to a blank clean mysql database set the coalition to latin 1 swedish.(iso 8859)
The newer versions support utf8
Give the database user global rights.
Also on a local host it is best to have a password for the db user, some have root with no password by default.

Then goto your ubbfolder and under includes edit config.inc.php and edit all the paths , passwords and users to match your current setup.
That is the quick version.

Read the wiki at:
https://www.ubbwiki.com/article/view/6/migration-guide.html

Last edited by Ruben; 07/21/2020 11:56 AM. Reason: corrected typo
Blue Man Group
There is no such thing as stupid questions. Just stupid answers