Update the datatable properties with the json data and redraw the table after a ajaxcallback

I am improving with datatables but i need a bit of help.
Maybe i am wrong, but i didnt find datatables examples working with Json data ( from server side processing ) not being the default data ( sEcho, iTotalRecords, iTotalDisplayRecords, aaData, [aoColumns] ) like

var debug;
...

"fnServerData": function ( sUrl, aoData, fnCallback, oSettings ) {
			oSettings.jqXHR = $.ajax( {
				"url":  sUrl,
				"data": aoData,
				"success": function (json) {
					if ( json.sError ) {
						oSettings.oApi._fnLog( oSettings, 0, json.sError );
					}

					$(oSettings.oInstance).trigger('xhr', [oSettings, json]);
					// MYCODE a simple example, i pass sTitle ( Columns titles ) on the json
					for (var property in json){
						if ( property == "aoColumns"){
							for (var aoColIndex in json["aoColumns"]){
								oSettings["aoColumns"][aoColIndex]["sTitle"] = json["aoColumns"][aoColIndex]["sTitle"];
							}
						}
					}
					//oSettings.oApi._fnAjaxUpdateDraw( oSettings, json);
					//oSettings.oApi._fnDraw( oSettings );
					debug["oSettings"] = oSettings;
					// ENDMYCODE it works but datatable isnt drawed
				},
				"dataType": "json",
				"cache": false,
				"type": oSettings.sServerMethod,
				"error": function (xhr, error, thrown) {
					if ( error == "parsererror" ) {
						oSettings.oApi._fnLog( oSettings, 0, "DataTables warning: JSON data from "+
							"server could not be parsed. This is caused by a JSON formatting error." );
					}
				}
			} );
		},
...
console.log( debug );

I think i know how pass the json, with the new properties data, and change the datatable properties with the new one, but datatable isnt draw/printed/refreshed.

I follow the right steps ?
I will change this code for a function that allow me to parse data from json and store on datatable.oSettings.

					for (var property in json){
						if ( property == "aoColumns"){
							for (var aoColIndex in json["aoColumns"]){
								oSettings["aoColumns"][aoColIndex]["sTitle"] = json["aoColumns"][aoColIndex]["sTitle"];
							}
						}
					}

Maybe u can tell me if there is already a funtion to do this.
I checked JQuery.dataTables.js library and i found many functions and things there but didnt find a function to do this.
But dont know, maybe i didnt see it.
I am a bit lost. I need some advices to do this.

I found "fnDrawCallback" and "fnPreDrawCallback" but still dont get it :(