These are due to permissions issue, as you are trying to delete the files while loggged in from user that is not the owner of those files.That www-data is server user, ask your server provider to remove those files or change the owner of files.
For this issue, you need to change the owner of the files. This command will work for you
sudo chown -R www-data:www-data /var/www/html
Run this command from your ssh and try again.
Regards
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