英文方法：
You can do the following:
sudo apt-get install python-software-properties
sudo LC_ALL=C.UTF-8 add-apt-repository ppa:ondrej/php
sudo apt-get update
Optionally purge PHP 5:
sudo apt-get remove php5-common -y
Or directly purge it including configuration files:
sudo apt-get purge php5-common -y
And finally install PHP 7:
sudo apt-get install php7.0 php7.0-fpm php7.0-mysql -y
Optionally clean up unneeded packages afterwards:
sudo apt-get --purge autoremove -y
Alternatively, you can install PHP 7.0 from sources using this script script or following instruction on this blog.