请让我知道如何在 Ubuntu 11.04 中删除某些存储库。更新时出现以下错误。
sudo apt-get update
Err http://ppa.launchpad.net natty/main Sources
404 Not Found
Err http://ppa.launchpad.net natty/main i386 Packages
404 Not Found
......
E: Some index files failed to download. They have been ignored, or old ones used instead.