I read about this in the press today, but can't find it anywhere within Facebook. Perhaps the feature isn't live yet? I've tried clearing cache and reloading, but don't know where I should be looking.
It's in Account → Account Settings, near the end of the page. Here's a video about how to use it and where to find it, but keep in mind that the option hasn't been rolled out to everyone yet, so you might not see it right now.