[kde-linux] Downgrade KDE SC Version 4.12.2

[Kanjana]

I am on Linux Mint 13 KDE 64-bit.

The update manager is set to levels 1, 2, 3 and 4.

Task-bar with application icons is/are completely missing after update. 
My customized wallpaper has changed to the Linux Mint Maya default 
wallpaper which appears to be somewhat oversized. Can only use Alt+F2 to 
access applications etc..

How can I safely remove 4.12.2 and reinstall an 'older' version?

Please help me!