Mate.How did you shear that bit off??
Anyway,to remove it,First undo the nut on the pinion shaft,(that's the bit that's broke) take the plate off the back of the diff casing and you will see the diff wheels and crown wheel.On either side of the unit is a cap held on with two bolts.Remove the caps and pull the whole unit out.You may need to use a couple of lever bars.Then the broken pinion can be removed.
Hope this helps Tonto.