Change Key Dynamically in Web.Config

System.Xml;
private void SetConfigSettings()
{
string path = Server.MapPath("Web.config");
string newConnectionString = @"Server=local;Database="+txtDatabaseName.Text+";Trusted_Connection=true";
XmlDocument xDoc = new XmlDocument();
xDoc.Load(path);
XmlNodeList nodeList = xDoc.GetElementsByTagName("appSettings");
XmlNodeList nodeAppSettings = nodeList[0].ChildNodes;
XmlAttributeCollection xmlAttCollection = nodeAppSettings[0].Attributes;
xmlAttCollection[0].InnerXml = txtKey.Text; // for key attribute
xmlAttCollection[1].InnerXml = newConnectionString; // for value attribute
xDoc.Save(path); // saves the web.config file
}