It's the first time I'm going to travel to the States. I applied for a ESTA VISA (I have a Spanish passport) and it was approved but now I realized that I only mentioned that I'm going to travel to New York (4 days) when I'm fact I'm going first to Hawai (12 days). Will I have any problem at the airport? Do I need to apply again or it doesn't matter? I'm trying to call a help number but everything is closed today. I appreciate a lot any help!!
No, it doesn't matter. Your ESTA is valid for travel anywhere in the United States and does not need to be updated if/when your plans change, you visit again, etc.
Of course, if questioned on arrival, you should answer truthfully, and I presume you're connecting via New York anyway since there are no direct flights from Spain to Hawaii