设置下载源

sudo vim /etc/apt/sources.list
用#注释之后输入
deb http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ stretch main contrib non-free rpi 
deb-src http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ stretch main contrib non-free rpi
esc加:wq保存并退出
后缀参照原先源设置镜像源

更改软件包索引
sudo vim /etc/apt/sources.list.d/raspi.list
deb http://mirror.tuna.tsinghua.edu.cn/raspberrypi/ stretch main ui
deb-src http://mirror.tuna.tsinghua.edu.cn/raspberrypi/ stretch main ui

然后更新
sudo apt-get update && sudo apt-get upgrade -y