Stay or upgrade

Hello everybody

I'm currently owning and using 4 out of 6 Norton Internet Security licenses.

I am currently thinking going for 8 more licences. Should I expand the current licenses ?  Or should I go for the Norton Security ones ?

I didn't found exactly the differences between NIS and NS, and if I choose to go on NS, does NIS uninstalls correctly from the computers and can I safely install NS ?

Thanks for your time