The content that comes with each new version of Poser is essentially geological in nature.  It is a new layer of sediment overlaying all of the previous layers.  If you store the content as a separate Runtime - with nothing else added, the new content can be its own new Runtime and you can remove the older Runtime.  If you added or altered the existing content -  back it up and load the new on top of it.  It is the same plus the new content.  Any new or altered files with different names will still be there.  In any case, there is no need to keep the earlier Runtime along with the new.  I think the more significant addition is Roxie and Rex.