update from a grid

[King Abadon]

I have this XML

<?xml version="1.0"?>
<Aparate>
	<Aparat>
		<Denumire>AF MARINCA  SAECO 1P</Denumire>     
		<NumarCitire>156</NumarCitire>
		<DataCitire>31.10.2007</DataCitire> 
		<ContorGeneralInitial>817</ContorGeneralInitial>
		<ContorGeneralFinal></ContorGeneralFinal>
		<Pozitii>
			<Pozitie>
				<Produs>Cafea espress</Produs>
				<ContorInitial>817</ContorInitial>
				<ContorFinal></ContorFinal>
			</Pozitie>
			<Pozitie>
				<Produs>Cafea cu lapte</Produs>
				<ContorInitial>317</ContorInitial>
				<ContorFinal></ContorFinal>
			</Pozitie>
		</Pozitii>
	</Aparat>
	<Aparat>
		<Denumire>LAVAZZA</Denumire>     
		<NumarCitire>112</NumarCitire>
		<DataCitire>31.10.2007</DataCitire> 
		<ContorGeneralInitial>144</ContorGeneralInitial>
		<ContorGeneralFinal></ContorGeneralFinal>
		<Pozitii>
			<Pozitie>
				<Produs>Cafea espress</Produs>
				<ContorInitial>817</ContorInitial>
				<ContorFinal></ContorFinal>
			</Pozitie>
			<Pozitie>
				<Produs>Cafea cu lapte</Produs>
				<ContorInitial>317</ContorInitial>
				<ContorFinal></ContorFinal>
			</Pozitie>
			<Pozitie>
				<Produs>Capucino</Produs>
				<ContorInitial>123</ContorInitial>
				<ContorFinal></ContorFinal>
			</Pozitie>
		</Pozitii>
	</Aparat>
</Aparate>

i put in a combo APARAt and i have 2 names(Denumire):AF MARINCA SAECO 1P and LAZAZZA

i filter a grid so when i change the combo in the grid i have the TAGS Pozitie for each APARAT.

i update the grid with data .How can i save it in the original XML.
this is my code

	XmlDbCommand command = new XmlDbCommand("SELECT * FROM Aparat WHERE Aparat.Denumire = '" + strValoare + "'", conn);
			XmlDbDataAdapter da = new XmlDbDataAdapter(command);
			DataTable tableAparat = new DataTable("Aparat");
			da.Fill(tableAparat);
            
            String Aparat_Id = String.Empty;
            for (int i = 0; i < tableAparat.Rows.Count; i++)
            {
                if (Aparat_Id != String.Empty)
                    Aparat_Id += " OR ";
                Aparat_Id += "Pozitii.Aparat_id = '" + Convert.ToString(Convert.ToInt32(tableAparat.Rows[i]["Aparat_Id"].ToString()) + 2) + "'";
            }

            command = new XmlDbCommand("SELECT * FROM Pozitii " + (Aparat_Id != String.Empty ? " WHERE " + Aparat_Id : ""), conn);
            da = new XmlDbDataAdapter(command);
            DataTable tablePozitii = new DataTable("Pozitii");
            da.Fill(tablePozitii);
            String Pozitii_Id = String.Empty;
            for (int i = 0; i < tablePozitii.Rows.Count; i++)
            {
                if (Pozitii_Id != String.Empty)
                    Pozitii_Id += " OR ";
                Pozitii_Id += "Pozitie.Pozitii_id = '" + Convert.ToString(Convert.ToInt32(tablePozitii.Rows[i]["Pozitii_Id"].ToString()) + 2) + "'";
            }

            command = new XmlDbCommand("SELECT * FROM Pozitie " + (Pozitii_Id != String.Empty ? " WHERE " + Pozitii_Id : ""), conn);
            da = new XmlDbDataAdapter(command);
            DataTable tablePozitie = new DataTable("Pozitie");
            da.Fill(tablePozitie);

            dgPozitii.DataSource = tablePozitie;

i'm using an XML provider.CAn you pls help me