Replacing Some Elements in XML [Sample XML Provided]

Question

I have an xml document that looks like this.I have a XML file structured as below. Sample XML is as follows:

Answer 1

var xdoc = XDocument.Load(path_to_xml);
var groupByName = xdoc.XPathSelectElement("//groupBy/name");
groupByName.Value = "STATE";
xdoc.Save(path_to_xml);