Stage 1 - hold the head in a pair of pliers and twist them whilst holding the figure
Stage 2 - the head then comes off with a clean break.
Stage 3 - use a pin to help locate the point for your drill.
Stage 4 - drill a hole in the body.
Stage 5 - superglue a piece of brass wire (or paper clip) in position.
I tend to use a much longer piece of wire and cut it down as it easier to locate and glue.
Prussian Officer ready for a new head and Saxon Officer - head donor - ready for his conversion.
Stage 6 - using the pin locate the drill point on the new head and then drill a hole. Cut down the wire and test whether there is a good fit between the new head and body. If not, drill some more or cut some more wire away and superglue the head on the pin.
Original Prussian Officer, new Prussian Officer and original Saxon Officer,
Only to be based to be the finished product.