So, you bashed a character in your book. You gave them horrible qualities and put those qualities under the microscope for all to see. Now they are clamoring to have their story told.
So now what? How do you turn around a character trait and take a character from dis-likable and make them your hero? I think the secret is to make them as real as possible. Make them as human as you can. No one is completely good or completely bad.
Give your character a reason to have had their bad habits and horrible qualities in the first place, then show the journey that they are taking to fix those quarks.
If you can do this readers will fall in love with characters they started out loving to hate.