Try re downloading it.
If you want to stop the update notifications for the failed one go to update history from the Control Panel right click on the failed download and choose hide. Then try to download again.
Hands-on: Samsung Galaxy S8 review
1995-2015: How technology has changed the world in 20 years
Samsung's beautifully designed Galaxy S8 makes for better VR experiences too
47 iPhone camera tips to help you take better photos
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.