I have installed kubuntu 14.04.3 in my laptop, when I check the version of kde its shows as follows,
When I tried sudo add-apt-repository ppa:neon/kf5
in terminal, am getting response as,
Cannot add PPA: 'ppa:neon/kf5'.
Please check that the PPA name or format is correct.
I wish to update kde into Plasma 5. How to solve it ?
Neon has been replaced by Kubuntu CI (https://launchpad.net/~kubuntu-ci/+archive/ubuntu/stable). In any case this is a release for KDE developers. There is also a new KDE Neon project which can serve to install up-to-date KDE, but is currently also only available as unstable release (and not intended for Kubuntu 14.04). http://neon.kde.org.uk/download
The solution is to update your Kubuntu to version 15.10 http://www.kubuntu.org/news/kubuntu-15-10/ which will give you a Plasma 5 version already.
Then you may add kubuntu-backports ppa to get recent bugfixes. The above mentioned KDE Neon project can then also be installed through a ppa, but be aware that this controversial project just started and stable releases are not yet available.
Possibly related question: Now when there is no neon/kf5 ppa, how can I install KDE 5 in gnome Ubuntu 14.04?