http://alioth.debian.org/docman/view.php/30192/21/debian-amd64-howto.html#id292796

Can I `apt-get arch-upgrade` from an already installed i386 debian?

No. You need to reinstall on a newly formatted partition or disk, by either running cdebootstrap / debootstrap from your running installation or using the Debian-Installer.


んー。なんか大変そうですね。