final gear oil change

ok guys or gals i need your help…..
trying to change final gear oil on my grizzly 550 and having a hell of a time … the drain bolt seems to be stuck on there really well i cant get it to budge.. ya think it would be ok to use a torch to heat it up or is that a bad idea … also i wanna make sure its the right bolt.. its an allen bolt right ?? and also dose anyone know the size of the filler bolt 19 is the bigest i have and its too small.. thanks for any help….