Please see the file /etc/apt/sources.list
Peruse the Debian method of marking [oldoldstable] [oldstable] [stable] [testing] [unstable] [experimental] and various other kinds.
Then find your installed Knoppix version's (not the Debian Current Version) declaration in the sources file at the very top.
Re-arrange your declarations accordingly. It is simple and common-sense.
Also don't forget to install the security keys by hand.
Can't be done unless you are Superuser.
That is all there is.
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