Upgrading Debian (Lenny) to Debian Squeeze

Debian Squeeze (stable) was released on February 6, 2011.

1. First update all packages which are currently installed

# apt-get update
# apt-get upgrade

2. Open /etc/apt/sources.list and replace all occurrences of lenny with squeeze

3. Update the apt repository

# apt-get update

4. Upgrade apt, dpkg and aptitude

# apt-get install apt dpkg aptitude

5. Upgrade the system

# apt-get dist-upgrade

It could be that grub is not being updated correctly, therefor do not forget to update grub.