To cut a long story, due to a lying cow of a mother I had to change my surname. This can be done by Statutory Declaration quite cheaply, and easily, fill in paperwork, pay the fee (iirc £30), swear on affidavit, job done, just ask at your local county court.
Just done some googling and apparently there is no legal process to changing your name, you just do it and notify who you need to (bank, dvla, etc)
My mate’s dad changed his name from Horace to Cyril. He said it was because Horace was a god awful name so we all couldn’t understand why the hell he picked Cyril.
I changed my surname when I was 18, had been known as for a few years, but couldn’t change it legally until I was 18. I changed from my birth surname to the that of the family I grew up with. I changed it back a few years later, personal reasons for doing so, didn’t use any legal paperwork the 2nd time, just informed bank, Dvla etc of my decision. It was made easier by the fact that I was reverting back to my birth surname, so already had proof if any was needed.