type
  ...
  bal=array [1..10] of real;
  TStud=record
        FIO: string [80];
        Year: TDateTime;
        MedB: bal;
        Kurs: byte;
        Group: byte;
  end;
  fil = file of TStud;
var
  f:fil;

procedure TDelete.SpeedButton1Click(Sender: TObject);
var k: byte;
//удаление записи
begin
  k := strtoint(edit1.Text);
  reset(f);
  seek(f, filesize(f) - 1); {1}
  read(f, s);                 {2}
  seek(f, k - 1);            {3}
  write(f, s);                 {4}
  seek(f, filesize(f) - 1);  {5}
  truncate(f);               {6}     
  closefile(f);
  displayall(MainForm.SGstud);
  Delete.close;
end;