This is a fairly critical procedure found in Ford factory service manuals that you must follow to ensure proper ball joint "preload" and good steering return. If not done correctly the ball joints may wear prematurely.
1. Torque lower nut to 40 ft-lbs.
2. Torque upper nut to 85-100 ft-lbs. If you cannot install the cotter pin, continue tightening to align the nearest hole in the stud with the castellation in the nut.
3. Final torque the lower nut to 95-110 ft-lbs.