John Lennon formally changed his middle name by deed poll from Winston to Ono, during a brief ceremony held on the roof of the Apple building at 3 Savile Row, London. The ceremony was carried out before Bueno de Mesquita, Commissioner of Oaths. Lennon had never liked his middle name, which had been given to him to serve as a wartime act of patriotism.

Technically, Lennon was unable to lose the Winston from his name, as UK law dictates that a person is unable to fully revoke a name given at birth.

More Info: en.wikipedia.org