update

$ apt-get update && apt-get upgrade

backup sources.list

$ cp /etc/apt/sources.list /etc/apt/sources.list.bak

replace `stretch` to `buster` of `/etc/apt/sources.list`

$ sed -i 's/stretch/buster/g' /etc/apt/sources.list

run upgrade

$ apt-get update && apt-get upgrade

run dist upgrade

$ apt-get dist-upgrade

$ reboot
$ lsb_release -a

clean:

$ apt-get autoremove