How to install CiviCRM patch (5.7.2 to 5.7.5) on Drupal 7.64 - is my file directory writeable?
For cpanel it's described in more detail at https://documentation.cpanel.net/display/76Docs/File+Manager#FileManager-Modifyfileorfolderpermissions

but briefly open the icon called File Manager and right-click on the folder and choose permissions.

In most shared hosting setups "writable by the webserver" means the user column has write access. Here "Drupal files" most likely means the "sites/default/files" subfolder.

But if you're upgrading and civi was working before it almost certainly has the right permissions already.

If you make backups first you'll usually be safe no matter what happens.