APT vorbereiten

# vi /etc/apt/sources.list


deb http://ftp.de.debian.org/debian/ stable main non-free contrib
deb-src http://ftp.de.debian.org/debian/ stable main non-free contrib

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

deb http://ftp.de.debian.org/debian/ stable-updates main contrib non-free
deb-src http://ftp.de.debian.org/debian/ stable-updates main contrib non-free

Mini upgrade

apt-get update
apt-get upgrade
reboot

Full upgrade

apt-get full-upgrade
reboot