How to clean the local package directory?

[David Arnstein]

My local package directory contains multiple versions of many cygwin
packages.  It also contains versions of packages that I no longer use.

What is the best procedure for cleaning up the local package
directory?  I very much want to preserve cygwin's notion of what
packages (and what versions thereof) I have installed.  It would be
very tedious if I had to pick and choose all the packages I want,
again.

Thanks for any suggestions!