How do I change the transmission fluid and the filter on my '77 F-150?

You can change the filter if you like but there really isn't a need. Purchase a case of ATF (Type "F" ) and a large drain pan. Remove the inspection cover on the lower part of the Bell-housing and rotate the engine until you see the Drain Plug on the Torque Converter. Remove the plug to drain. Remove all of the bolts from the Transmission pan to access the remaining fluid and the filter. Replace the gasket, filter, drain plug and inspection covers. Add 5 quarts of ATF to the Transmission and start the motor. Add 5 more quarts, move the Gear selector through ALL of the gears and recheck the fluid level. Drive (not idle) the vehicle until warm and recheck trans fluid level. Done.

Or you can pay maybe eighty bucks or so at a garage, not get dirty, have to dispose of the fluid, not greese up the garage floor or driveway, and be on your way in about an hour.