Upgrade Debian to a new release

Performing a full system upgrade in Debian, most of the time works without any problem. But make a full backup of your files if something goes wrong.

Edit the source.list file that contains Debian repositories

sudo vim /etc/apt/source.list

The repository list should looks like follow

deb http://deb.debian.org/debian bullseye main contrib non-free
deb-src http://deb.debian.org/debian bullseye main contrib non-free

deb http://deb.debian.org/debian-security/ bullseye-security main contrib non-free
deb-src http://deb.debian.org/debian-security/ bullseye-security main contrib non-free

deb http://deb.debian.org/debian bullseye-updates main contrib non-free
deb-src http://deb.debian.org/debian bullseye-updates main contrib non-free

Close and save the changes in the source.list file, then refresh apt

sudo apt update

After that, performs a full system upgrade

sudo apt full-upgrade

Then run this commands to clean and remove everything that the system don't need anymore

sudo apt autoclean

sudo apt autoremove

At last reboot the system

sudo reboot

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