Since there is no simple way to install Plasma desktop themes in KDE I've written this short tutorial on how to do it manually.
First, there are several themes available in the PCLOS repositories. Open Synaptic and do a search for plasma theme and you'll find the following themes available:

Some people will be satisfied with those themes. I, however, prefer a much larger variety of themes to be available. Unfortunately there is no easy option for installing Plasma desktop themes, so it is something that needs to be done 'manually'. Fortunately it's a very simple process.
Plasma desktop themes can be found at
http://kde-look.org/. Once you have selected and downloaded your theme(s) of choice follow these instructions to install it.
1. Open a console(Kmenu >> More Applications >> Terminals >> Konsole).
2.
cd into the directory where you saved the plasma theme.
3. Type in the following to extract the tarballed plasma theme:
For .tar.gz
tar -zxf plasma_theme.tar.gzFor .tar.bz2
tar -xjf plasma_theme.tar.bz24. This should create a folder with the name of the plasma theme. Type in
ls to list the files in the directory.
5. Type in
su and then enter your root password to go into
Super User Mode.
** IMPORTANT ** While in Super User Mode you will have no restrictions and can do anything to your computer. It is highly recommended that you use Super User Mode only when absolutely necessary and that you EXIT out of Super User Mode AS SOON AS YOU ARE DONE your task in order to minimize any damage you could accidentally inflict on your system.6. Enter the following command to move the plasma theme folder to the proper directory:
mv plasma-theme /usr/share/apps/desktoptheme7. Type in
exit to quit
Super User Mode.
That's it! Now open System Settings and check out your new theme. If you had System Settings open during this process you will probably need to restart System Settings to see new additions to your Plasma desktop themes. Below is an example of a Plasma desktop theme being installed using the
K-TATTOO theme as an example.
