Yes you would only if you transferred your 3.23 mysql database across. In Windows you can just install 4.x, stop the service, change the ini file to the relevant path you want (say the D: drive or something like that) and then copy/move all the databases (3.23.x) to the new location. Starting the service again will use the new mysql database. In that case yes an upgrade is due as mentioned above. If however you just move all the databases and keep the mysql used from the fresh installation of 4.x there is no need to run the script.
