Well, so far I've looked up and read the constitution of the US, several state constitutions in all of the iterations from the articles of confederation to current times, read several encyclopedia articles, and am about a couple of hours away from calling up my history major friend.
So far I haven't found anything that specifically layed it out.
I've seen the figures for voting on state constitutions, but how to vote on federal constitutions and amendments isn't layed out in those (that I've read).
I've read the constitution, but it doesn't say anything but that two thirds of the states must ratify it. It doesn't say how.