I installed Knoppix 2 months ago. Now I want to upgrade. Should I reinstall Knoppix, or should I just do 'apt-get upgrade' ?

In my sources.list, I see the following unofficial Debian sources, so I am afraid I might bread my system if I do 'apt-get upgrade'.

'deb ftp://ftp.kde.org/pub/kde/stable/latest/Debian/sid ./
deb-src ftp://ftp.kde.org/pub/kde/stable/latest/Debian/sid/ ./

# kdevelop
deb http://people.debian.org/~njordan kde3.0-woody/