1.备份并打开sources.list

sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup

sudo gedit /etc/apt/sources.list

2.替换源地址

阿里源：

# deb cdrom:[Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)]/ xenial main restricted

deb-src http://archive.ubuntu.com/ubuntu xenial main restricted #Added by software-properties

deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted

deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted multiverse universe #Added by software-properties

deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted

deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted multiverse universe #Added by software-properties

deb http://mirrors.aliyun.com/ubuntu/ xenial universe

deb http://mirrors.aliyun.com/ubuntu/ xenial-updates universe

deb http://mirrors.aliyun.com/ubuntu/ xenial multiverse

deb http://mirrors.aliyun.com/ubuntu/ xenial-updates multiverse

deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse

deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse #Added by software-properties

deb http://archive.canonical.com/ubuntu xenial partner

deb-src http://archive.canonical.com/ubuntu xenial partner

deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted

deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted multiverse universe #Added by software-properties

deb http://mirrors.aliyun.com/ubuntu/ xenial-security universe

deb http://mirrors.aliyun.com/ubuntu/ xenial-security multiverse

清华大学源地址：

https://mirrors.tuna.tsinghua.edu.cn/help/ubuntu/

3.保存并更新sources.list

sudo apt-getupdate