Winston fits Orwell's definition of a hero. Winston shows himself a hero, first, by embarking on the path of decency and modeling what that looks like for us. He becomes the change he wants to see. Later, he shows his heroism in being willing to sacrifice himself to join an underground movement against the state.
As the novel opens, Winston is filled with a seething anger. His buying and writing in a journal, two subversive acts, signal his willingness to fight back against the system, even if his rebellion is ultimately futile.
However, at this point, Winston has internalized the dehumanization and violence of his society. For instance, although he is sexually attracted to Julia (though he doesn't yet know her name), in his fantasies he wants to rape and kill her. As he later tells her:
I wanted to rape you and then murder you afterwards. Two weeks ago I thought seriously of smashing your head in with a cobblestone.
He also enjoys a graphically violent movie that he writes about in his journal, noting
a wonderful shot of a child’s arm going up up up right up into the air ...
He also callously kicks aside a hand a bomb has blown off somebody:
When he got up to it he saw that it was a human hand severed at the wrist. Apart from the bloody stump, the hand was so completely whitened as to resemble a plaster cast. He kicked the thing into the gutter ...
However, once he falls in love with Julia, and they begin, as often as they can, to experience an old-fashioned domestic life in the room about Mr. Carrington's shop, Winston changes. He becomes gentler and more protective, now that he has someone to love and care about who is more important to him than himself. He is even able to see the fat prole woman who hangs the laundry in the courtyard below as a beautiful human being. He regains his humanity—perhaps the most heroic thing, according to Orwell's notion of decency, he could have done.
He also is willing to sacrifice himself for a rebellion that might never come to fruition in his lifetime. He makes a mistake is in agreeing to all sorts of violence, such as throwing acid in another person's face, to bring the revolution around, but his courage and his heart are in the right place. He knows that what he is doing—agreeing to engage in revolution and engaging in a love relationship with a woman unsanctioned by the state (which would never sanction such a thing)—has doomed him, but he is willing to face his death.
In the end, Winston is broken (except is he? Right before he cries over Big Brother he remembers a happy time playing Snakes and Ladders with his mother and sister), but whether or not the state destroyed him, he has nevertheless shown his heroism in his prior actions.