Configure Web Service to respond in JSON

good day. I recently developed a WS with several methods, which connect to SQL server. I am trying to consume them through Ajax, researching this topic I found that to perform this action, my WS must respond in JSON format, I understand that natively the WS (developed in Visual) responds in XML format. My doubts are: Is it correct that to consume WS by Ajax, it has to respond in JSON? and the second question is how I configure my WS to respond in JSON format. Attached code of a method:

[WebMethod]
    public String[] InsertxWEBUsers(Session _session, xWEBUsers _xWEBUsers)
    {
        SqlConnection con = new SqlConnection();

        try
        {
            con = this.conection(_session);

            this.check(con);

            xWEBUsers ReleasexWEBUsers = this.initxWEBUsers(con, _xWEBUsers);

            con.Open();

            if (this.validateField(ReleasexWEBUsers.cpnyid.Trim(), ReleasexWEBUsers.custId.Trim(), ReleasexWEBUsers.userId.Trim(), con))
            {
                this.throwException("El UserId " + ReleasexWEBUsers.userId.Trim() + " ya existe en la compañia " + ReleasexWEBUsers.cpnyid.Trim() + " y en el cliente " + ReleasexWEBUsers.custId.Trim() +"");
            }

            this.validatexWEBUsers(ReleasexWEBUsers, con);

            SqlCommand cmd = this.commandInsertxWEBUsers(ReleasexWEBUsers, con);
            cmd.ExecuteNonQuery();


        }

        finally
        {
            con.Close();
        }
        return strArray;
    }

As additional information, researching the internet I found JSON.net a kind of complement to get the WS to respond in JSON, but even so it did not work.

I appreciate your attention, and I remain attentive to your comments, thank you.

Greetings !!!

Annex the Ajax call to invoke my Ws:

$.ajax({
    type: "POST",
    url: "http://devsyshyperv6:8080/xWSRMSUser.asmx/StatusxWEBUsers",
    data: "{ session: '" + session + "', xwEBUsers: " + xwEBUsers + "}",
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: function(r) {
        alert(r.d);
    },
    error: function(r) {
        alert(r.responseText);
    },
    failure: function(r) {
        alert(r.responseText);
    }
});
return false;

Is it correct?