On the 2004 Accord that filter is very easy.

Open the glovebox & empty it. Unclip the little strut so the glovebox can hinge way down - upside down. You don't have to remove the glovebox, just let it hang upside down on it's own hinge.

Behind where the glovebox WAS, is the black plastic air ducts. There's a cover that snaps out to reveal the cabin air filter. Slide it out...