一、备份源列表
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
二、命令行打开sources.list文件
sudo vim /etc/apt/sources.list
三、修改sources.list文件
sudo vim /etc/apt/sources.list
将源文件内容全部注释，并添加以下内容任意源
deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
1 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted 2 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted 3 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal universe 4 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates universe 5 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal multiverse 6 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates multiverse 7 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse 8 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted 9 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security universe 10 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security multiverse
四、保存：ESC+：wq！
五、更新源
sudo apt-get update
六、更新软件，然后你就可以感受到更换国内源之后的飞速提升了
sudo apt-get dist-upgrade
sudo apt-get upgrade