My skin of hands and neck is too rough and black may be due to exposed to sunlight. How can I cure i?

See a dermatologist. You may also have a condition called acanthosis nigricans which could be related to an underlying endocrine (hormonal) disorder. See a dermatologist.
Need exam. There are several possibilities including contact dermatitis, allergic reaction to chemicals, photo dermatitis, and conditions such as lupus, or a rare condition such as dermatomyositis. Over the counter cream will not be effective in an advanced case and it best to see a dermatologist for proper diagnosis and treatment.