permissions needed to rename themes and plugins wordpress folders

 One of our wordpress websites was not entering recovery mode. 

... email from Wordpress regarding a fatal error while doing a setting in the menu using Astra theme. We had encountered such an error earlier also but could recover the site through the recovery link. However today on clicking on the recovery link it says recovery not initialized. ...

So, we had to disable plugins in order to be able to access the site. To follow the SSH/SFTP method described in this page - https://kinsta.com/knowledgebase/disable-wordpress-plugins/

But ... files could be opened but cannot rename since it says permission denied

So, just adding the ssh user to the www-data group was not enough - 

sudo adduser  thewordpresswebsiteadminuser www-data

also had to chmod the parent directory to 775 - was 755 earlier. 

cd theparentdirectory 
chmod -R 775 *

Then renaming worked.