打开终端,在终端下输入
sudo cp /etc/apt/sources.list  /etc/apt/sources.list.backup
/* 备份旧的源到/etc/apt/sources.list.backup */
sudo gedit /etc/apt/sources.list
/* 用gedit编辑sources.list,gedit可以换成vim等其它编辑器 */
选择sources.list里面的全部内容删除。

将两行###之间的内容复制进去(这个是广东的源,不错)
#################################################################
deb http://ubuntu.dormforce.net/ubuntu/ intrepid main multiverse restricted universe
deb http://ubuntu.dormforce.net/ubuntu/ intrepid-backports main multiverse restricted universe
deb http://ubuntu.dormforce.net/ubuntu/ intrepid-proposed main multiverse restricted universe
deb http://ubuntu.dormforce.net/ubuntu/ intrepid-security main multiverse restricted universe
deb http://ubuntu.dormforce.net/ubuntu/ intrepid-updates main multiverse restricted universe
deb-src http://ubuntu.dormforce.net/ubuntu/ intrepid main multiverse restricted universe
deb-src http://ubuntu.dormforce.net/ubuntu/ intrepid-backports main multiverse restricted universe
deb-src http://ubuntu.dormforce.net/ubuntu/ intrepid-proposed main multiverse restricted universe
deb-src http://ubuntu.dormforce.net/ubuntu/ intrepid-security main multiverse restricted universe
deb-src http://ubuntu.dormforce.net/ubuntu/ intrepid-updates main multiverse restricted universe
###########################################################################
保存退出

终端下运行
sudo apt-get update
进行下更新
完毕!