video xss :)
You're already on Google.//Here is the variable with which you assign a new value to the attribute
string newValue = string.Empty;
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load(xmlFile);
XmlNode node = xmlDoc.SelectSingleNode("Root/Node/Element");
node.Attributes[0].Value = newValue;
xmlDoc.Save(xmlFile);