While it is customary for a woman to adopt her husband's surname, there is no legal requirement to do so.
You may wish to:
If it is one of the latter two options you will need to change your name by deed poll
You will also need to obtain a new passport from the UK Passport Service if you are changing your surname.
If you are not a British citizen your country may require you to firstly sign a legal document at their embassy or consulate to initiate a change of name. Please telephone them first.