You have a legal right to change your title to Miss, Ms or Mrs when you change your name. You can apply for a deed poll if you have decided to acquire a certain gender for your life. This deed poll will help you to change your title on all your documents.
Please note, that deed poll does not certify the change of your gender. In order to legally change your gender you need to obtain Gender Recognition Certificate. Also, changing your title does not signify a change in your marital status. Adding Mrs to your title does not make you a married person.