Removing files from Drupal is more tricky than you might think. There has been another tutorial about this using the module File Delete. It requires going through a cycle of minimum 6 hours. By default, Drupal protects files from removal which are still being used and referenced in other content. Instead of directly deleting a file, the linked usages need to be cleared first, and the files marked as temporary, then finally the system will remove them during cleanup.
This is actually a good policy. However, sometimes it’s annoying to wait for a few hours before these files are being cleaned up. In particular, if we are sure these files are unused or orphaned, there is another module called Fancy File Delete, which solves this problem.
Fancy File Delete allows you to delete files straight away without having to wait.
However, great care must be taken when using this module, because it has a ‘force delete’ option. Use of this module should be restricted to experienced administrators.