Levels will most likely help you there.
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When I deal with handwriting, I usually copy it into an alpha channel and invert it, then use levels to take out the paper texture and strengthen the handwriting. Then I convert that into a selection and fill it into a new (normal) layer or into a mask for a new layer. That way you have transparency and better control over everything.
But if you don't want to do all that, adjusting the levels at least should help. 🙂