One of my little toenail is all dark brown for as long as i can remember? how can o get rid of it?

Brown nail: As you state the nail stays brown even as it grows out this usually eliminates a bruise staining the nail. It sounds like fungus which means a visit to your podiatrist is in order . While there methods of dealing with fungus can be discussed

Matricectomy: Depends if there is fungus, can treat with topicalmeds, oral antifungals, or combination of both oral and topical. Also laser treatment is effective or complete matricectomy.