Check Debian Version on Debian website:
https://www.debian.org/releases/
Check version on system:
$ sudo lsb_release -a No LSB modules are available. Distributor ID: Debian Description: Debian GNU/Linux 11 (bullseye) Release: 11 Codename: bullseye
Or
$ sudo cat /etc/os-release
USERS SHOULD BACKUP ALL DATA before attempting a release upgrade – SEE https://wiki.debian.org/DebianStability
Only after the back – do the following:
Ensure your system is up-to-date in it’s current release.
$ sudo apt update $ sudo apt upgrade
If you haven’t already, ensure all backups are up-to-date.
Make a backup of the /etc/apt/sources.list file:
$ sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
In a text editor, replace the codename of your release with that of the next release in APT’s package sources
For instance, the line:
deb https://deb.debian.org/debian/ buster main
should be replaced with
deb https://deb.debian.org/debian/ bullseye main
$ sudo nano /etc/apt/sources.list
# Clean and update package lists
$ sudo apt clean $ sudo apt update
Perform the major release upgrade, removing packages if required
$ sudo apt full-upgrade
Remove packages that are not required anymore. Be sure to review this list: you may want to keep some of them
$ sudo apt autoremove
Reboot to make changes effective (optional, but recommended)
$ sudo shutdown -r now