OpenFileDialog opendialog = new OpenFileDialog();
opendialog.Filter = "Access database|*.accdb";
if (opendialog.ShowDialog() == System.Windows.Forms.DialogResult.OK)
{
OleDbConnectionStringBuilder bui = new OleDbConnectionStringBuilder(conn.ConnectionString);
bui.DataSource = opendialog.FileName;
conn.ConnectionString = bui.ConnectionString;
}