Webservice asmx does not return JSON, only XML

Question

I wanted to solve this problem, the return of my webservice, returns with the JSON body, but the XML header. how do I return the structure in JSON ?

I’ve read all the internet and can’t understand, I saw some jQuery scripts with ASP.NET but my application is in C#, someone has some idea ?

Follow my consultation return:

<?xml version="1.0" encoding="UTF-8"?>
<string xmlns="http://tempuri.org/">[{"id_produto":"27","nr_referencia":"1","nm_produto":"SKOL 600ML","path_foto":"","qtd_estoque":"