Uninstalling/reinstalling Poser will not get rid of the 3rd party content you already installed.  You will need to uninstall Poser and then completely delete the primary Poser folder or move the residual folders to another location before reinstalling Poser.  But performing the latter will certainly break many things.  If you have the original content files archived separately from your computer, my suggestion delete everything and start afresh, installing what you really need or want and reserving the rest for projects; no use installing content that you will use once or never use.  However, if you have very old content, you will need to address and convert the old thumbnail .RSR file format to .PNG file format.