how to restore database in sql server

   string BackFileName = "";
            OpenFileDialog objOFD = new OpenFileDialog();
            objOFD.CheckFileExists = true;
            objOFD.Filter = "Backup Files (*.bak)|*.bak";
            if (objOFD.ShowDialog().ToString() == "OK")
            {
                string ext = objOFD.FileName.ToString().Substring(objOFD.FileName.ToString().LastIndexOf('.') + 1);
                if (ext == "bak")
                {
                    BackFileName = objOFD.FileName;
                }
                else if (ext == "")
                {
                    BackFileName = objOFD.FileName + ".bak";
                }
                if (conn.RestoreDB(BackFileName))
                {
                    MessageBox.Show("DataBase Restore suceessfully");
                }
                else
                {
                    MessageBox.Show("Error in restoring DataBase", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
            }