Precise location can vary slightly, so you'll likely need a repair manual specific to your 2004 Pontiac Grand Am to pinpoint the exact location and the steps to access it. A Haynes or Chilton manual would be helpful. Online forums specific to Grand Ams might also have pictures or descriptions to help.
Caution: Working on the BCM involves electrical components. If you're not comfortable with automotive electrical systems, it's best to have a qualified mechanic perform any repairs or replacements.