I have had to take over multiple projects that were years out of date on multiple platforms/os/languages. It's a nightmare that one does not wish on anybody, it

I have had to take over multiple projects that were years out of date on multiple platforms/os/languages. It's a nightmare that one does not wish on anybody, it's possible but as the other poster notes, one has to have extensive testing suite to verify functionality before and after - or one has to make one to have any hope of succeeding (making a final product up to date and functioning correctly unless one just wants to make something just run.) It's never as easy as just changing the lib/imports since active languages/libraries are living things, to say nothing of dead libraries that one has to update or replace.