It doesn't look like it will be easily improved by cleaning as the patina doesn't look very stable. You might try to flick off a piece with a pin around his face just to see what happens.
This coin has some heavy environmental damage, the large spot by the face appear to be active bronze disease. It should be removed, but I'm afraid it has already damaged the coin.
Here is what I came up with after applying my limited knowledge of coin treatment. I am reluctant to take it further, but I think better job can be done. Wether it is pheasible, I do not know.
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