1.安装wget

yum install wget

2.备份原来的源

cd /etc/yum.repos.d
mv CentOS-Base.repo CentOS-Base.repo.bak

3.下载替换源

wget http://mirrors.163.com/.help/CentOS7-Base-163.repo
mv CentOS7-Base-163.repo /etc/yum.repos.d/CentOS-Base.repo

4.清理缓存

yum clean all
yum makecache

5.更新系统

yum update -y