files are not writable

Hello, how do I fix following things? It says it’s ‘critical’

Some files are not writable by WordPress:
xmlrpc.php
wp-blog-header.php
readme.html
wp-signup.php
index.php
wp-cron.php
wp-config-sample.php
wp-login.php
wp-settings.php
license.txt
wp-mail.php
wp-links-opml.php
wp-load.php
wp-includes/class-wp-user-query.php
wp-includes/l10n.php
wp-includes/date.php
wp-includes/class-wp-oembed.php
wp-includes/images/w-logo-blue-white-bg.png
wp-includes/images/blank.gif
wp-includes/images/down_arrow.gif
…