Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
Most of the shops are flushing them these days, but that is not always the best thing to do. I personally would rather replace the filter as well. There are ways to flush it with 2 buckets and some long rubber hoses. Then again, if it has not been done on a regular basis it could be worse than just leaving it alone. If the fluid has been changed in the past, then I would do a fluid and filter change on it.
Refer to the Maintenance Schedules in Maintenance, for proper service intervals. The fluid capacity of the 45RFE is approximately 13.25 liters (14.0 quarts). REMOVAL
INSPECTION Inspect bottom of pan and magnet for excessive amounts of metal. A light coating of clutch material on the bottom of the pan does not indicate a problem unless accompanied by a slipping condition or shift lag. If fluid and pan are contaminated with excessive amounts or debris, refer to Testing and Inspection. CLEANING
NOTE: Do not attempt to install the seal onto the oil filter first and then into the oil pump. An unsatisfactory seal between the oil pump and filter will result, allowing air to be drawn into the pump.