"Old versions" are versions up to CMSimple 3.4. These versions are ANSI encoded and do not have a pagedata.php.
Basically, it is recommended to prepare the update either on a local server environment or in a subdirectory on the Web server.
If everything works fine, you can copy the new installation to the place, where the old website was, or lead the domain to the new directory on the server side.
Updates from CMSimple_XH up to version 1.5.3 to the current version of CMSimple are much simpler than an update to the current version of CMSimple_XH.
The contents of CMSimple_XH 1.6 and later are no longer compatible with CMSimple, switching from CMSimple_XH 1.6 or higher to CMSimple is conversion to a completely different CMS.