do-release-upgrade fails: Ubuntu 12.04.5 LTS

Hello,

How do I update the sources for update?

I followed these instructions:

~~[https://www.linode.com/docs/security/upgrading/how-to-upgrade-to-ubuntu-14-04-lts" target="_blank">](https://www.linode.com/docs/security/up … -14-04-lts">https://www.linode.com/docs/security/upgrading/how-to-upgrade-to-ubuntu-14-04-lts](

do-release-upgrade fails because sources are not found.

examples from /var/log/dist-upgrade/main.log

, W:Failed to fetch ~~[http://old-releases.ubuntu.com/ubuntu/dists/precise-updates/main/source/Sources" target="_blank">](http://old-releases.ubuntu.com/ubuntu/d … ce/Sources">http://old-releases.ubuntu.com/ubuntu/dists/precise-updates/main/source/Sources]( 404 Not Found

, W:Failed to fetch ~~[http://old-releases.ubuntu.com/ubuntu/dists/precise-updates/restricted/source/Sources" target="_blank">](http://old-releases.ubuntu.com/ubuntu/d … ce/Sources">http://old-releases.ubuntu.com/ubuntu/dists/precise-updates/restricted/source/Sources]( 404 Not Found

Can I edit sources.list to fix errors, and perform upgrade?

Thank you.