Record of Name Change from the 1970's

Hi,

My parents divorced in HK in the early 70's and my mother remarried an American on or about 01 January 1974 and she took his surname. My surname was also changed around the same time to match my new step-father's. I'm a British Citizen (born in the UK) and would have been seven years old at the time.

I'm looking to get a certified copy of my name change but I'm not having much luck finding anything online. I can see where there are applications for birth, death and marriage certificates but nothing I can see for a name change. I'm hoping someone here can point me in the right direction.

Thanks,
Steve