Debian 12

cat << 'EOF' > /root/upgrade_to_v12.sh
#!/usr/bin/env bash

# set Version
sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list
sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list.d/*

# Update
apt-get -y update
apt-get -y upgrade
apt-get -y dist-upgrade
apt autoclean
apt autoremove
apt --purge autoremove

# you may add/update -> /etc/apt/sources.list
# deb http://security.debian.org/debian-security/ bookworm-security main
# deb-src http://security.debian.org/debian-security/ bookworm-security main

exit 0
EOF

chmod u+x /root/upgrade_to_v12.sh