步骤如下：

1.更新原有系统

sudo apt-get update
sudo apt-get upgrade

更改源

vim /etc/apt/sources.list

备份原有的源，替换成如下的：

deb http://ftp.us.debian.org/debian/ wheezy main
deb-src http://ftp.us.debian.org/debian/ wheezy main

deb http://security.debian.org/ wheezy/updates main
deb-src http://security.debian.org/ wheezy/updates main

# wheezy-updates, previously known as 'volatile'
deb http://ftp.us.debian.org/debian/ wheezy-updates main
deb-src http://ftp.us.debian.org/debian/ wheezy-updates main

更新新的源列表

sudo apt-get update

安装需要的包

sudo apt-get install apt dpkg aptitude

升级

sudo apt-get dist-upgrade

完成，此时可以用如下命令验证：

lsb_release -a

为了更好的运行新系统，建议重启系统：

reboot