Files that are locked on a WebDAV connection cannot be modified by any other WebDAV connection.
Right-click the locked file you want to unlock from those listed in the
WebDAV connection's node in the Navigator pane, then choose Unlock.
OR
Select the locked file you want to unlock from those listed in the WebDAV connection's node in the Navigator pane, then choose File | WebDAV | Unlock.
Select the file that you want to unlock, from those listed in the List
Locks pane, then choose File | WebDAV | Unlock.
A list of the files that you are about to unlock is displayed in the Unlock
Files dialog.
Click OK to unlock the listed files.
Files that were previously locked that are now unlocked are display the
unlocked 
icon
in the Navigator pane.