This question already has an answer here:
I currently have ubuntu 12.04 and when I try to update the version 14.04 after a while appears that message:
W:Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/hardy/universe/source/Sources 404 Not Found [IP: 188.8.131.52 80] W:Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/hardy/multiverse/source/Sources 404 Not Found [IP: 184.108.40.206 80] E:Some index files failed to download. They have been ignored, or old ones used instead.
Then the upgrading process stops.
How can I resolve this?