What is the right way, to update a perl-from-sourcefile-installation?

"Your first sentence seems to be contradicted by the second. Do you maintain your Perl via your linux distribution's package manager, or do you build it from source?

If you build from source, simply download the new distribution, build it and install it like you did the first time. It will overwrite old versions of executables and libraries with new ones as needed, but won't delete anything you have installed via CPAN.

There's no trick to it really."