兄弟们，教我一下，如何替换文件中的内容呀？(0分)

比如
"VBS - VBTCP,PC4","02/06/2002","20:15:56","9","C"
"VBS - VBTCP,PC4","02/06/2002","20:17:15","9","C"
"VBS - VBTCP,PC4","02/06/2002","20:18:46","9","C"
我要用将“9”替换成“0”，应该用的是什么涵数呀？

procedure TForm1.ReplaceDialog1Replace(Sender: TObject);

var
SelPos: Integer;
begin
with TReplaceDialog(Sender) do
begin
{ Perform a global case-sensitive search for FindText in Memo1 }
SelPos := Pos(FindText, Memo1.Lines.Text);
if SelPos > 0 then
begin
Memo1.SelStart := SelPos - 1;
Memo1.SelLength := Length(FindText);
{ Replace selected text with ReplaceText }
Memo1.SelText := ReplaceText;
end
else MessageDlg(Concat('Could not find "', FindText, '" in Memo1.'), mtError, [mbOk], 0);

end;

end;

错，不合我的意思。
不知writeln可否实现，就是说，当指针到9这个位置时，将0写进去。
如何实现，我不需要什么MEM导来导去的！！！！烦！！！！