Which file for "Configuring Automatic Background Updates"

I follow these instructions to perform updates:
http://codex.wordpress.org/Upgrading_WordPress

There is a new link to this page about “Configuring Automatic Background Updates” http://codex.wordpress.org/Configuring_Automatic_Background_Updates

So, which file is this page actually talking about placing parameters in? I have read through the page a few times, and still do not know where to begin actually setting my preferences. TIA!