My OS: Linux Mint 13 KDE 64-bit.
The update manager was set to levels 1, 2, 3 and 4.

The update manager prompted to update 218 packages which was successfully completed. I closed the update manager. Firefox and Thunderbird were working and all appeared to be okay.

However after restarting the computer I was prompted to enter my password although I enabled Auto-Login a long time ago.

Well, I entered my password and then noticed that my customised wallpaper had changed to the Linux Mint Maya default wallpaper which appears to be somewhat oversized.
The desktop has no taskbar anymore, I left/right click the desktop but no responses.

However I am able to press Alt+F2 to open the Application Launcher Menu.

I double-checked the monitor resolution settings in both 'Size & Orientation' and 'NVIDIA settings' which has not changed and still is 1360x768.

According to KInfo Centre the KDE SC Version is now 4.12.2 and I suspect that this particular update/upgrade is the culprit.

I kindly request an expert guiding hand to remove safely version 4.12.2 and to re-install a previous version of KDE (I forget what my previous version was).

Many thanks in advance.