1. 备份原来的镜像源/etc/apt/source.list文件

cp /etc/apt/sources.list /etc/apt/sources.list.bak

2. 编辑文件：

vim /etc/apt/sources.list

3. 删除所有记录

在命令行模式下dd删除一行，按住d可以持续删除

4. 添加阿里云：

注意系统版本，本版本为Ubuntu20

deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse

# deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
# deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
# deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
# deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse

## Pre-released source, not recommended.
# 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

5. 运行更新

apt update

6. 完成

参考：https://midoq.github.io/2022/05/30/Ubuntu20-04%E6%9B%B4%E6%8D%A2%E5%9B%BD%E5%86%85%E9%95%9C%E5%83%8F%E6%BA%90/