you do whats called a free "push" within the same registrar, the new owner can create a free account at the same registrar to take the push, you then push it to his/her username , this transaction is instant. Secondly , the new owner can transfer it to his/her registrar of choice by filling out a request transfer form for the domain , at which time you would unlock it and recieve an email from your registrar with a authorization code to confirm the transfer, takes usually 5 days and the new owner has to pay another year registration fee.