I want to change my first name its spelled wrong... example My name is Martina and they put Marta. How can I fix this?

Where do you live now? How old are you.

But no, your name is Marta, and that is the legal name you should have always been using, your nickname may be Martina but that is not your name. What you want and need to do, is make a name change to the name you want. (assuming you are an adult) Each nation or state if in US, has its own law on how to do this. It does not actually change your birth certificate but it does legally change your name.

Martina and they put Marta.

Normally, in the US, you file a petition in court (the state court for the state in which you reside or, if you are in PR, the courts of the Commonwealth of PR).