uses Jpeg;
....
procedure ConvertJpegToBmp(const FileNmJpg: TFileName; const IsReplace: Boolean=False);
var B: TBitMap; J: TJpegImage;
begin
 J:=TJpegImage.Create;
 try
  J.LoadFromFile(FileNmJpg);
  B:=TBitmap.Create;
  try
   B.Width:=J.Width;
   B.Height:=J.Height;
..........
   B.Canvas.Draw(0, 0, J);
   B.SaveToFile(ChangeFileExt(FileNmJpg, '.bmp'));
   if IsReplace then DeleteFile(FileNmJpg);
  finally
   B.Free;
  end;
 finally
  J.Free;
 end;
end;

ConvertJpegToBmp('name.jpg');