1. Edit sources.list
sudo vi /etc/apt/sources.list
and change all words etch to lenny, or stable to testing (vim:
2. Update and upgrade
sudo aptitude update sudo aptitude install apt dpkg aptitude sudo aptitude full-upgrade
that is all, this also work if you want to go from lenny to sid, just change your sources.list accordingly.
It is also better if you start your Debian Linux in text mode, so GDM or KDM could be restarted without problems.
After the upgrade: