Problem with protected files…

Hi… I’m having trouble with some files in the “Status report” in “Reports” link at the back end…

In the configuration section I got this message

Not protected
Protection disabled
The file sites/default/settings.php is not protected from modifications and poses a security risk. You must change the file’s permissions to be non-writable.
The file sites/default/settings.local.php is not protected from modifications and poses a security risk. You must change the file’s permissions to be non-writable.

I tried to fix it doing:

chmod 644 sites/default/settings.local.php
chmod 644 sites/default/settings.php

I also tried :
chmod 755 sites/default

But files belongs to the group www-data and his owner is my user (victorarango) which is not a member of www-data

But I still recieve the same message…

I’m using Ubuntu 16.04 with PHP Version 5.6.26-2+deb.sury.org~trusty+1

Drupal version: 


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