Manually disable locking state:

• put ownCloud in maintenance mode: edit config/config.php and change this line:
  'maintenance' => true,
• Empty table oc_file_locks: Use tools such as phpmyadmin or connect directly to your database and run:
  DELETE FROM oc_file_locks WHERE 1
• disable maintenance mode (undo first step).

Source: File is locked – how to unlock – FAQ – ownCloud Central