As part of your transition, you may choose a new name that better fits your identity. You can choose any name you like and you are free to use it day-to-day, whenever and however you like. If you intend to use this name as your legal name, you will need to change it by using a deed poll.
A deed poll is a form that you can fill-in that legally changes your name. You can use it to change your first and last name, as well as any middle names you might have.
A deed poll is free to complete and you can download a template online. You'll need to fill out your details and sign the document, which will need to be witnessed and signed by two other people. You need to be 16 or over to complete a deed poll.
Some organisations might require you to have an 'enrolled deed poll'. This is where your name change has been registered with the Royal Courts of Justice. This will cost £36 and you will need to send the application by post.
It is a good idea to print and sign multiple deed polls, because if you use them to change your details on numerous forms of ID, such as a driver's licence or passport, they may not send it back.
You can find more information on deed polls, including enrolled deed polls, here.