Maintenance for the week of January 12:
• PC/Mac: No maintenance – January 12
• ESO Store and Account System for maintenance – January 13, 9:00AM EST (14:00 UTC) - 12:00PM EST (17:00 UTC)
If you have a locked file or insufficient file access privilege it's most likely a Windows Administrator issue OR....another program has that file open so it cannot be changed/deleted/accessed by ESO.
If you are running Steam try not running it and making sure Steam is completely closed out (look in Task Manager to be sure) and try updating again.