asp.net web forms json return result

I use asp.net and web forms. In my project I have asmx web service

[WebMethod]
    public string GetSomething()
    {
      // avoid circual reference(parent child)
      List<RetUsers> res = repo.GetAllUser().Select(c => new RetUsers {User_ID = c.User_ID,User_Name = c.User_Name,Date_Expire = c.Date_Expire }).ToList();
      string res1 = res.ToJson();
      // extension methods
      return res.ToJson();
    }

And result is in this format.

[
    {"User_ID":1,"User_Name":"Test 1","Date_Expire":null},
    {"User_ID":2,"User_Name":"Test 2","Date_Expire":null}
]

How can I append to label this result in $.ajax sucess to get this output:

1 - Test 1, 2 - Test 2.

Return the list instead, and use [ScriptMethod(ResponseFormat = ResponseFormat.Json)] attribute - it will create JSON object as return automatically:

[WebMethod]
[ScriptMethod(ResponseFormat = ResponseFormat.Json)] 
public List<RetUsers> GetSomething()
{
  // avoid circual reference(parent child)
  List<RetUsers> res = repo.GetAllUser().Select(c => new RetUsers {User_ID = c.User_ID,User_Name = c.User_Name,Date_Expire = c.Date_Expire }).ToList();

  return res;
}

And on JS side:

$.ajax(
{
    type: "POST",
async: true,
url: YourMethodUrl,
data: {some data},
contentType: "application/json; charset=utf-8",
dataType: "json",
    success: function(msg)
    {
        var resultAsJson = msg.d // your return result is JS array
        // Now you can loop over the array to get each object
        for(var i in resultAsJson)
        {
            var user = resultAsJson[i]
            var user_name = user.User_Name
            // Here you append that value to your label
        }
    }
})