There are avenues to appeal to the service for an upgrade to your discharge level, including up to Federal court (although that is more of a last resort). Make sure you have all your service records, if not, then you should write to the Department of the Navy to get them. An attorney can help you prepare an appeal. Another poster recommended William Cassara (www.williamcassara.com), I can personally recommend Bill as well. Bill practices exclusively in military law and is very good at it.
There are many lawyers that practice in this area, check out the websites, reputations and rates of a few attorneys and see if they can help you out.
This answer does not, nor is it intended to, create an attorney-client relationship, but is offered solely for informational purposes. Since the facts of each case are different, it is important to seek out qualified counsel with whom information can be shared and assessed under an attorney-client privilege so that competent and tailored advice can be provided.