question

Because I notice that you are using Unity Engine, please import these for convenience:

using PlayFab;
using PlayFab.ClientModels;

I will provide a sample here, and be aware that you can only use admin API and server API to upload title data.

Usuario myUsuario = new Usuario() { usuario = "testtest", /*....initialize your instance*/};
string myJsonString = JsonUtility.ToJson(myUsuario);
PlayFabServerAPI.SetTitleData(
	new PlayFab.ServerModels.SetTitleDataRequest {
		Key= "Usuario",
		Value= myJsonString 
	},
	Onsuccess=> {},
	Onfail=> {Onfail.GenerateErrorReport();} 
);

So in the game manager you will get a title data entry with key set as “Usuario” and value set as “{"usuario":" testtest "……}”

BTW, if you trying to get title data, you are able to use client API,

// after you login successfully
PlayFabClientAPI.GetTitleData(
	newGetTitleDataRequest {
		Keys = newList<string> { "YourDataKey" } 
	},
	OnSuccess => 
	{
		var yourObject = JsonUtility.FromJson<Usuario>(OnSuccess.Data["YourDataKey"]); 
	},
	OnFail => { });