Cannot update adGroupadfields

[Nick]

Hi,
I am trying to change Adtexts but i cant change anything except the
status.
I 've read that AdGroupAd's fields are not changeble.
Is that true?
So i can't update an adText?
Please help me...

this is my code:
$adService = $user->GetAdGroupAdService();
$AdGroupAdNEW = new AdGroupAd();
$AdGroupAdNEW->adGroupId = xxxxxxxxxx;
$AdGroupAdNEW->status = 'PAUSED';
$AdGroupAdNEW->ad = new TextAd();
$AdGroupAdNEW->ad->id= xxxxxxxxxx;
$AdGroupAdNEW->ad->url='http://www.test.com';
$AdGroupAdNEW->ad->displayUrl='http://www.test.com';
$AdGroupAdNEW->ad->headline='This is my title';
$AdGroupAdNEW->ad->description1='This is my desc1.1';
$AdGroupAdNEW->ad->description2='This is my desc2.1';
$operations = new AdGroupAdOperation($AdGroupAdNEW,NULL,'SET');
$adgroupAdReturnValue = $adService->mutate($operations);

[AdWords API Advisor]

Hi Nick,

That is correct, only the status of an ad can be changed. If you need
to change other fields you must create a new ad and delete the old ad.

Best,
- Eric Koleda, AdWords API Team