You need to use apt-get to install and automatically resolve dependency problems. See the sticky at the top of this forum.

It's not uncommon, though, to run into problems when doing a major upgrade of Knoppix (and updating KDE is major). My recommendation (well, my first recommendation would be to install Kanotix, but.......) is to point your apt-get sources to unstable, then run apt-get update, then update KDE.

As I say, do some searching and do read the sticky first.