Last saturday the Debian project has released the last version of the "universal operating system": the clean install, using updated CD images is one of the best and simple solution, however also the upgrade process is very simple and fast.

Ideally, you should follow the (long) upgrade workflow in the official documntation, but if your Debian 9 installation doesn't have any strange configuration in APT sources (yes, a 'frankendebian') you may perform the upgrade with four simple steps:

1. Modify the file /etc/apt/sources.list, anche change the release from "stretch" to "buster":


deb stretch main non-free contrib
deb-src stretch main non-free contrib
deb stretch/updates main contrib non-free
deb-src stretch/updates main contrib non-free


deb buster main non-free contrib
deb-src buster main non-free contrib
deb buster/updates main contrib non-free
deb-src buster/updates main contrib non-free

2. Update the package list:

# apt update

3. Make a full upgrade:

# apt full-upgrade

4. Finally, perform a cleanup of old packages:

# apt autoremove && apt autoclean

That's all, folks!