Just go a bit at a time and make sure you test fit as you go and you should be fine. If you go too far Pock's tutorial is definitely the best way to fix it.
Looks like you'd just need to dremell out the head till it fits on the neck ball. Dunno if the head has a peg in it but it looks like it does, either heat the head and pull out the peg or if it's moulded on just cut the peg off then dremell the head out.
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