I personally would get rid of the HP stuff that isn't used and then I'd removed the Medievals that you don't use or haven't played in ages.
If they're on Steam you can always just re-download them again or just re-install if you have them on disc.
But other than that, surely you can tell what you don't use and just remove that?
Also, any Steam games you have installed which you either don't play or haven't played in ages, then uninstall them.
If you're gonna want to play them later then you can re-download.