Perhaps I have not expressed myself clear enough.
I follow the instructions to the letter, as I have done so many times before over the last decade or so that I have used and upgraded to successive versions.
Among the steps, as pr the instructions, is to make a backup, a new copy, of the database which is named according to version. The configuration file is also copied and after the database name, user and password has been edited to reflect the new copy of the database. This amended configuration file is the uploaded in the var sub-directory, in the new installation, as directed.
Commencing the upgrade, the process obviously recognizes the database and all, hence the warning which is about something about the database. Usually the upgrade will continue smoothly but stops, and what is it about some old entries anyway? As the new code base is a fresh clone of the preexisting one, which is still the live version, it surely has all the details needed.
In any case, heeding the warning, even though it does not make much sense, I indeed tried putting the preexisting configuration file (with the older data base info) in the var folder instead as the prompt seem to suggest. That didn’t make any difference, it still does budge.
Second option was to try and change the table prefixes. That only produced an empty installation, functioning apparently but with no content.