help me legally change my name

hello, I'm Megan and I'm 18 years old. since I was 15 years old, I have identified as non binary, I came out to my family a few months ago as non binary. I've seen a psychologist who confirmed I have no issues relating gender and changing my name will most likely bring me to being more true to myself. being in therapy made me realise that I'm actually agender, still non binary but I don't want to identify as male or female just a human and who I am!! Alex is the name I've chosen because it's a gender neutral name! people calling me alex makes me so happy inside!! to change my name legally it will cost €400. every penny would mean the absolute world to me!!!