Can you change first names too, or does the law only apply to last names?

Yes, it applies to both first and last names. Although parents more commonly are disputing the child’s last name, the law equally applies to first names and uses the same standards. 

That was the issue in Munguia v. Ornelas, 253 Ariz. 549 (App. 2022), where the Father asked for the child’s first names to also include the Father’s requested first name. The trial court granted his request, and Mother appealed. The Arizona Court of Appeals held that the Pizziconi factors apply to both first and last names, analyzed those factors, and then upheld the trial court’s order.