Hello Readers !!

Here is the second method to read the XML file.

using UnityEngine;
using System.Collections;
using System.Xml;
using System.Collections.Generic;

public class XMLParsing : MonoBehaviour 
{
    public TextMesh fileDataTextbox;
    private string path;
    private string fileInfo;
    private XmlDocument xmlDoc;
    private WWW www;
    private TextAsset textXml;
    private List<Player> Players;
    private string fileName;

    // Structure for mainitaing the player information
    struct Player
    {
        public int Id;
        public string name;
        public int score;
    };

    void Awake()
    {
        fileName = "DemoXmlFile";
        Players = new List<Player>(); // initalize player list
        fileDataTextbox.text = "";
    }
    
    void Start ()
    {
        loadXMLFromAssest();
        readXml();
    }
    // Following method load xml file from resouces folder under Assets
    private void loadXMLFromAssest()
    {
        xmlDoc = new XmlDocument();
        if(System.IO.File.Exists(getPath()))
        {
            xmlDoc.LoadXml(System.IO.File.ReadAllText(getPath()));
        }
        else
        {
            textXml = (TextAsset)Resources.Load(fileName, typeof(TextAsset));
            xmlDoc.LoadXml(textXml.text);
        }
    }
    
    void Update()
    {
        // Following code just check whether any button is touched on mouse down
        if(Input.GetMouseButtonDown(0))
        {
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            RaycastHit hit;
            if(Physics.Raycast(ray, out hit) && hit.collider != null)
            {
                if(hit.collider.name.Equals("ModifyXmlButton"))
                    modifyXml();
                else if(hit.collider.name.Equals("CreateElementButton"))
                    createElement();
            }
        }
    }
    // Following method reads the xml file and display its content 
    private void readXml()
    {
        foreach(XmlElement node in xmlDoc.SelectNodes("Players/Player"))
        {
            Player tempPlayer = new Player();
            tempPlayer.Id = int.Parse(node.GetAttribute("id"));
            tempPlayer.name = node.SelectSingleNode("name").InnerText;
            tempPlayer.score = int.Parse(node.SelectSingleNode("score").InnerText);
            Players.Add(tempPlayer);
            displayPlayeData(tempPlayer);
        }
    }
    private void displayPlayeData(Player tempPlayer)
    {
        fileDataTextbox.text += tempPlayer.Id + "\t\t" + tempPlayer.name + "\t\t" + tempPlayer.score + "\n";
    }

    // Following method will be called by tapping ModifyXml button
    // It just multiply player's score by 10
    private void modifyXml()
    {
        fileDataTextbox.text = "";
        foreach(XmlElement node in xmlDoc.SelectNodes("Players/Player"))
        {
            int nodeId = int.Parse(node.GetAttribute("id"));
            Player tempPlayer = Players[nodeId-1];
            tempPlayer.score *= 10;
            Players[nodeId-1] = tempPlayer;
            node.SelectSingleNode("score").InnerText = tempPlayer.score + "";
            displayPlayeData(tempPlayer);
        }
        xmlDoc.Save(getPath()+".xml");
    }

    // Following method create new element of player
    private void createElement()
    {
        Player tempPlayer = new Player();
        tempPlayer.Id = Players.Count+1;
        tempPlayer.name = "Player"+tempPlayer.Id;
        tempPlayer.score = tempPlayer.Id*10;
        Players.Add(tempPlayer);
        displayPlayeData(tempPlayer);

        XmlNode parentNode = xmlDoc.SelectSingleNode("Players");
        XmlElement element = xmlDoc.CreateElement("Player");
        element.SetAttribute("id",tempPlayer.Id.ToString());
        element.AppendChild(createNodeByName("name",tempPlayer.name));
        element.AppendChild(createNodeByName("score",tempPlayer.score.ToString()));
        parentNode.AppendChild(element);
        xmlDoc.Save(getPath()+".xml");
    }
    private XmlNode createNodeByName(string name, string innerText)
    {
        XmlNode node = xmlDoc.CreateElement(name);
        node.InnerText = innerText;
        return node;
    }

    // Following method is used to retrive the relative path as device platform
    private string getPath(){
        #if UNITY_EDITOR
        return Application.dataPath +"/Resources/"+fileName;
        #elif UNITY_ANDROID
        return Application.persistentDataPath+fileName;
        #elif UNITY_IPHONE
        return GetiPhoneDocumentsPath()+"/"+fileName;
        #else
        return Application.dataPath +"/"+ fileName;
        #endif
    }
    private string GetiPhoneDocumentsPath()
    {
        // Strip "/Data" from path 
        string path = Application.dataPath.Substring(0, Application.dataPath.Length - 5);
        // Strip application name 
        path = path.Substring(0, path.LastIndexOf('/'));
        return path + "/Documents";
    }
}

Use this and be happy.

Keep coding.