HI,
Do you want to set the ../@CheckNo field value to the "filename" field?
if yes ,Please implement the code given by shiva with a little change
XMLNode fileNameNode = XDocument.DOM.selectSingleNode("<FileName node path>");
XMLNode CheckNode = XDocument.DOM.selectSingleNode("<checkNo node path>");
//Here which value you want to set that value need to get first and assign that value to this node
fileNameNode.text = CheckNode.text;
what you want is not the above mentioned one ,then please explain clearly about problem so that we can definitely help you.