Method 1:
Go to Applications ->Ubuntu software center
Type kubuntu-desktop in search field and install Kubuntu Plasma Desktop system.
Method 2:
Go to System ->Administration ->Synaptic Package Manager
Type kubuntu-desktop in search field. Right click kubuntu-desktop and select mark for installation and click Mark button.Then click Apply button.
After KDE finishes installing, log out.Then, before you log back in again, select KDE.
Note: native Gnome applications will be available in KDE, and native KDE applications will be available in Gnome.
