If a folder is empty, you can delete the folders outside of Windows using My Computer or Windows Explorer (not Internet Explorer).

If you're only deleting content from within Poser, you're not getting all of it. Poser content gets installed in so many different folders that it's hard to delete all of it. If you delete a character, there are also likely to be poses, props, and expressions for the character in the other libraries. Even if you get all that, there are still geometries and textures.

One neat trick with newer DAZ files is reinstalling the content from the executable and saying yes to creating an uninstallation file. After the installation, run the uninstaller to remove all the files (assuming that you didn't move them from their default locations in the original install). Older DAZ files don't do that and few freebies do. I've had to manually delete those files. It's possible that there might be a better way of handling those. I've just gotten into the practice of only installing content that I'm going to immediately use rather than install everything I get (I'd need a terabyte drive if I were to do that).

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon