5.2 Preparing for upgrade

You can upgrade from one distribution to another one by fetching packages over the network. This can be done as follows.

Get a clean list of repositories for stable:

     # cd /etc/apt
     # cp -f sources.list sources.list.old
     # :>sources.list  
     # apt-setup noprobe

If you want to upgrade to testing then add testing sources to this new list. If you want to upgrade to unstable then also add unstable sources.

     # cd /etc/apt
     # grep -e "^deb " sources.list >srcs
     # :>sources.list  
     # cp -f srcs sources.list
     # sed -e "s/stable/testing/" srcs >>sources.list
     # sed -e "s/stable/unstable/" srcs >>sources.list
     # apt-get update
     # apt-get install apt apt-utils

See Beginning Debian package management, Section 6.2 for the art of tuning /etc/apt/sources.list and /etc/apt/preferences.