From The 747-400 Flight Crew Training Manual,
press the TO/GA or set manual go-around thrust and select flaps 20 while rotating to the go-around attitude. As the thrust levers are advanced, auto-speedbrakes retract and auto-brakes disarm.
This is in the case of a rejected manual landing.
For an autoland, an auto go-around cannot be initiated after touch-down or if the airplane is below 5 feet radio for more than 2 seconds.
Only ever done it during simulator base-checks where the instructor selects flaps 20, winds the trim forward to approx. take-off setting and stands-up the thrust levers. While this is being done, the trainee keeps the aircraft on the centre-line and once the flaps are at 20 rotates on command from the instructor. Similar to the -200, except more tasks for the instructor!