Updating the already created rdf file

[Faisal Sarfraz]

Hi All
I am new to jena. I am trying to update RDF file which is placed
externally. Currently i am using this code to write it

String fileName = "details.rdf";
        FileWriter out = new FileWriter( fileName );
        try {
            model.write( out, "RDF/XML-ABBREV" );
        }
        finally {
           try {
               out.close();
           }
           catch (IOException closeException) {
               // ignore
           }
        }

this is writing it to external file now i want to update it after certain
changes. is there a way?
Please help