File editor permission

Hello,

I was able to edit files of the theme I’m using on 3.9, but I’m not able to edit the files anymore in the 4.0 version.

I’m using Apache with the default user and group (www-data). All the files are under that user and group. I tried changing the file permissions to 777 in all the theme but I keep getting the same message about permission change.

Any help?

Thank you in advance.