http://www.netfoucs.com/c80486/article/details/8460251 --失效
http://www.shumeipaiba.com/wanpai/jiaocheng/16.html
http://www.raspbian.org/RaspbianMirrors

1. 备份原镜像源定义文件

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

2. 修改镜像源定义文件
sudo vim /etc/apt/sources.list

原文件内容:
deb http://mirrordirector.raspbian.org/raspbian/ wheezy main contrib non-free rpi

修改为:(注意地址最后是没有斜杠的)
deb http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ jessie main contrib non-free rpi

deb http://mirror.nus.edu.sg/raspbian/raspbian wheezy main contrib non-free rpi
或

deb http://mirrors.aliyun.com/raspbian/raspbian/ wheezy main non-free contrib