See https://wiki.debian.org/DebianUnstable.
Basically (as root):
su -
cat <<EOF >/etc/apt/sources.list deb http://deb.debian.org/debian unstable main deb http://deb.debian.org/debian-debug unstable-debug main deb http://deb.debian.org/debian-ports unstable main EOF apt-get update apt-get -y dist-upgrade
Then answer the questions.