Many peole think that you are stuck with the name on your birth certificate and can only change it by deed poll or by a statutory declaration - both of which cost money.
You can change your name to whatever you want - it's called an assumed name - and it is legal.
An example is a relative of mine. On her birth cert her name was Mary-Jane White. When she was 4 her mum married Mr Brown and they started calling her Mary-Jane Brown. When she applied for her 1st passport all she had to do was submit a letter with it (I think her GP wrote it) saying that she had been known as Mary -Jane Brown since the age of four. Her bank account, driving licence etc were all in the name of Brown. When she was in her late teens she fell out with her stepdad and decided to change her name back to White. She sent copies of her birth cert to DVLA/the bank etc and found the procedure easy.
Just to confuse matters further, when she was 20 she decided she hated her double barrelled forenames and changed them to Alison. We thought that was the end of it until she met her future husband whose surname was Allison. She decided that Alison Allison would sound silly so she changed her forename yet again - she is now called Emma.......for the time being!
Phew!