linux-apt-dist-upgrade

/etc/apt/sources.list
    deb http://http.us.debian.org/debian stable main contrib non-free
     deb http://non-us.debian.org/debian-non-US stable/non-US main contrib non-free
     deb http://security.debian.org stable/updates main contrib non-free
     
     apt update
     apt install -sf
     apt keep-all
     apt dist-upgrade


of course you can also just browse:
http://ftp.uk.debian.org/debian/

or http://http.us.debian.org/debian  and see what they have

e.g. etch, lenny=stable, squeeze=testing for next major release, sid=unstable, 

http://en.wikipedia.org/wiki/Debian

e.g. http://en.wikipedia.org/wiki/Sidux