If it matters, I'm using the S88 Mk1 with KK2.9.6.
Well then, if you don't use products then you can uninstall them.
Well, it depends. Maybe some more context would help. Why do you want to uninstall these? Are you using Kontakt 6 or 7 in your old projects? Only a few DAWs have an auto-migration system for plug-ins like Kontakt, Cubase, Logic, Pro Tools and Maschine. Notes about Auto-Migration of Kontakt Versions in DAW Projects
Honestly, Battery 4 is the only app I'm using, and I don't even use that from within KK. That's about as much as I can say. 1 reason for that is I use mostly traditional samples of real instruments, as opposed to synths.
If you're looking to uninstall one of their products (such as software like Kontakt, Maschine, or others), you can follow the instructions provided on their support page.