like everyone's said, buy some hair dye, magic cannot alter your DNA. magic is energy found in nature, we use it in spells to aid us in life. how is having blond hair going to help you? perhaps an illusion spell might make your hair appear lighter to others, but there won't be any actual change.
Jesus, the only ay your getting blonde her is buying hair dye, magick can not change our DNA like they said above, its impossible, this is who we are and no one can change that.
just get some hair dye and it will be fine :)