From http://www.phoronix.com/forums/forum/software/desktop-linux/848907-kde-neon-is-now-live-providing-bleeding-edge-kde-packages-for-ubuntu?p=849059#post849059 Directions for installation on the NEON website are wrong in some parts and more complex than needed in other ones. 1. Traditional way to download and install a repository authentication key is "wget -q -O - 'http://archive.neon.kde.org.uk/public.key' | sudo apt-key add -" all in one line with no temporary file left behind. 2. The "sudo apt update" is to by typed on a new command line, not on the same one as apt-add-repository 3. The command "sudo apt install neon-desktop" didn't pull all the needed packages as I already have Kubuntu 15.10, all the needed packages were kept on hold to avoid incoherencies. I had to run more than once "apt-get -y install" with those held back packages (the package list was too long), then run "apt-get upgrade" and finally the usual "apt-get -y autoremove" and "apt-get -y clean" in order to try to get a "clean" upgrade. Reproducible: Always Steps to Reproduce: Already explained in the description Actual Results: . Expected Results: . .
I think what you need for #3 is sudo apt-get dist-upgrade. I'm also not sure why #2 needs a different console.
Cheers. The instructions should be fixed and more streamlined now. I am pretty sure 3. would be caused by having had a Kubuntu PPA at some point, which would then cause trouble with KDE neon as version expectancy doesn't line up anymore.