To find the correct capacity, you must identify the transmission type. This information is usually found on a tag on the transmission itself (often near the bellhousing) or in your owner's manual. Common transmission types for that year might include a C6, E4OD, or others.
Once you know the transmission type, you can search online (e.g., using Google, a parts website like AutoZone or Napa, or a Ford-specific forum) for the correct fluid capacity for a fill and a complete drain and refill. Always be sure to verify the information with multiple sources.