This step-by-step guide on debian i386 to amd64 conversion was really handy. I was in a hurry and needed clear and concise instructions.

My only trouble with the procedure was on the last step. My initrd image was built with bad libraries and refused to boot.

I had to update /etc/ld.so.conf and /etc/ld.so.d and rebuild the initrd from a rescue system (mkinitramfs).

Kudos to Stefanos Harhalakis for the howto.