use a 6 point socket or wrench. do it with a hot engine, but check access to all bolts with cold engine. start from the outside and go in. do not remove any completely until you are sure all will come free. once all the manifold to head bolts are loose, but before removing them, remove the pipe to manifold bolts. it wont matter if they break if you are putting on headers.
the head bolts should come loose fairly easily. they are only spec'd around 65 ft/lbs, so if you use a 1 foot ratchet, that's not a lot of force. also sometimes it helps to tighten just a tad before loosening.
