Отвечаю сам на свой вопрос:

## Код:
```
var
   oldPath: String;

//////////////////////////////////

function GetOldPath(): String;
var
  sUnInstPath: String;
  sOldPath: String;
begin
  sUnInstPath := ExpandConstant('Software\Microsoft\Windows\CurrentVersion\Uninstall\Моя программа_is1');
  sOldPath := '';
  if not RegQueryStringValue(HKLM, sUnInstPath, 'Inno Setup: App Path', sOldPath) then
    RegQueryStringValue(HKCU, sUnInstPath, 'Inno Setup: App Path', sOldPath);
  Result := ExpandConstant(sOldPath);
end;

///////////////////////////////////

procedure CopyRegFiles;

var
  FL: TFindRec;
  pt1,pt2 : String;
begin
   pt1 := AddBackslash(OldPath);
   pt2 := AddBackslash(ExpandConstant('{app}'));

    if (Length(oldPath) > 0) and (pt1 <> pt2) then
    begin
       try

           if FindFirst(pt1 + '*.xyz', FL) then
           begin
              repeat
       FileCopy(pt1 + FL.Name, pt2 +  FL.Name,False);
              until not FindNext(FL);
           end;
        finally
                     FindClose(FL);
        end;

    end;

end;
/////////////////////////////////
//function UnInstallOldVersion(): Integer;
//.........
//end;

procedure CurStepChanged(CurStep: TSetupStep);
begin
  if (CurStep=ssInstall) then
  begin
     oldPath := GetOldPath;
     //UnInstallOldVersion();

  end;

  if (CurStep=ssPostInstall) then
  begin
     CopyRegFiles;
  end;

end;
```
