使用 update-manager 进行跨版本升级。确保已经安装 update-manager。
1.首先，修改源
sudo gedit /etc/apt/sources.list
替换为以下内容：
（本文以升级到ubuntu 13.04 为例。每一个版本都有对应的标识）
#deb http://archive.ubuntu.com/ubuntu/ raring main restricted universe multiverse
#deb http://archive.ubuntu.com/ubuntu/ raring-security main restricted universe multiverse
#deb http://archive.ubuntu.com/ubuntu/ raring-updates main restricted universe multiverse
#deb http://archive.ubuntu.com/ubuntu/ raring-proposed main restricted universe multiverse
#deb http://archive.ubuntu.com/ubuntu/ raring-backports main restricted universe multiverse
#deb-src http://archive.ubuntu.com/ubuntu/ raring main restricted universe multiverse
#deb-src http://archive.ubuntu.com/ubuntu/ raring-security main restricted universe multiverse
#deb-src http://archive.ubuntu.com/ubuntu/ raring-updates main restricted universe multiverse
#deb-src http://archive.ubuntu.com/ubuntu/ raring-proposed main restricted universe multiverse
#deb-src http://archive.ubuntu.com/ubuntu/ raring-backports main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ quantal main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ quantal-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ quantal-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ quantal-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ quantal-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ quantal main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ quantal-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ quantal-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ quantal-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ quantal-backports main restricted universe multiverse
2.检查更新
sudo apt-get update
3.下载更新
sudo apt-get -d dist-upgrade //-d 表示只下载
4.跨版本升级
sudo update-manager -d // 按照提示，选择‘部分更新’
完成之后，先不要重启，在重新试一下
sudo apt-get update
sudo apt-get upgrade
确保全部升级完成。
5.重启完成跨版本升级
6.清除旧文件
sudo apt-get autoremove
sudo apt-get autoclean
换源，从Ubuntu 15.04升级到Ubuntu 15.10“Wily Werewolf”：http://www.linuxdiyf.com/linux/11975.html
Ubuntu 13.04升级至Ubuntu 13.10（服务器版）教程：http://www.linuxdiyf.com/linux/12022.html
ubuntu14.04升级到ubuntu15.04方法：http://www.linuxdiyf.com/linux/11803.html