First and foremost you need to go to this website if you are looking to either sell or buy WOW accounts.  Then you enter into live chat with a representative to get a quote.  Give the representative all information about character as well as any information you feel is important about your account.  You and a representative agree on a price, you will need to submit account information, a valid identification and your personal contact information.  Don't worry, all personal information is secure and will never be forwarded to another user.  Once all information is verified in the account has a new e-mail address, payment will be necessary.