name change

My new husband has a son from previous relationship(never married to her) in which he had a son.He goes by his middle name & does not know his 1st name.The biological mother has no contact, she left hospital by herself & my husband left with his child which he raised until we met.He wants to change his 1st name that he doesnt like & has bad memories to him.His son does not know this name.He needs to do something soon because the child will be going to kindergarten next year.We are in Pa.He has no idea her exact address, just somewhere in Pa.What are his options? Is this feasible to do or is he gonna have to learn to live with the name she gave him as her last stab in his back?

Just out of curiosity, what is the childs first name? Is it that bad? I don't know how to go about changing the first name but when they go to school, they are usually asked what name they go by. Example, nickname, middle name and so on. If the parent informs the teacher that he goes by his middle name, that is what they will call him.