I want to update it via DOS, but intel information on the site are confusing and imprecise.
I'd forget about a DOS update with this board. Before you go down the path of attempting an update, why do you want (or need) to perform the update? If it's to correct this freezing on Intel splash screen problem, I can categorically tell you a BIOS update is not what's required!
What brought on that problem (ie what changes have you made leading up to it)?
Eventually when you've resolved the underlying problem causing the freezing at BIOS splash screen (and NOT before), if you still want to update the BIOS, the 'Recovery using a CDROM' method that's explained in the Readme PDF file that's available on the download page would be the method I'd choose for an update in THIS CASE. If THAT is still to confusing then I suggest you liase with a computer shop and ask them to do the work for you. You don't want to be messing about attempting BIOS upgrades unless you're confident that you know what you're doing as there is a potential to kill the board if procedures aren't followed.