debian7是 ubuntu12同期的版本，可以算是比较老了，升级可以参看这个 https://wiki.debian.org/LTS/Using
1.修改/etc/apt/source.list
deb http://deb.debian.org/debian/ jessie main contrib non-free
deb-src http://deb.debian.org/debian/ jessie main contrib non-free
deb http://security.debian.org/ jessie/updates main contrib non-free
deb-src http://security.debian.org/ jessie/updates main contrib non-free
2.apt-get update && apt-get -V upgrade
3.apt-get dist-upgrade
4.reboot
5.apt-get autoremove
debian8 升级 debian9 参见 https://www.linuxidc.com/Linux/2017-12/149050.htm