what i did was enter regedit in my windows start menu… then I’d go to
Computer\HKEY_LOCAL_MACHINE\SOFTWARE
and from there I would just delete all the plugins i didn’t have in my computer anymore… like I had an old string for Kontakt I would delete that inside the native instruments folder… i had a seperate folder for izotope plugin demos, I just deleted the whole string.
you must know what is in your own computer to make it work. if you remove to much you might get problems… at worst maybe you must reinstall some stuff 
good luck - this is the best I can explain it for you. but at least for me now I have a bunch of samples in media bay, and all is now quick again - at times I could wait over 2 minutes for some presets to display, now its as good as instant