I've been asked this question a few times recently so it really must be an essay question! See https://www.theanneboleynfiles.com/q-a/in-your-opinion-how-have-perceptions-and-images-of-anne-boleyn-and-significant-moments-in-her-life-changed-throughout-history/ for my answer.
Personal bias does come into it, as does religion - Nicholas Sander attempted to blacken her name and he was a Catholic in exile during the reign of Anne's daughter, Elizabeth I. John Foxe was a Protestant writing about Protestant martyrs in Elizabeth I's reign so Anne was a martyr in his eyes.
I hope that gives you a starting point.