How to change selected row in datatable?

I have another problem. I have binded datagridview, and when I doubleclick on row in it all cell values are "transformed" into textboxes. What I wanna do is when I change textbox value there also have to be made changes in datagridview and datatable. So far I get to change only first row of datagridview, not the selected. Here is my code:

private void buttonEdit_Click(object sender, EventArgs e)
    {
        int i = 0;
        foreach (DataGridViewRow row in dataGridView1.SelectedRows)
        {
            for (int j = 0; j < dataGridView1.ColumnCount; ++j)
            {
               competitorDataSet.Growns.Rows[i][j] = row.Cells[j].Value;
            }
++j;

                }
                competitorDataSet.Growns.Rows[i][0] = textStN.Text;
                competitorDataSet.Growns.Rows[i][1] = textN.Text;
                competitorDataSet.Growns.Rows[i][2] = textSN.Text;
                competitorDataSet.Growns.Rows[i][3] = textC.Text;
                competitorDataSet.Growns.Rows[i][4] = textYB.Text;
                this.grownsBindingSource.EndEdit();
                if (dataGridView1.BindingContext[competitorDataSet.Growns] != null)
                {
                    dataGridView1.BindingContext[competitorDataSet.Growns].EndCurrentEdit();
                }
                this.competitorDataSet.Growns.AcceptChanges();