I want to update the PHP version of Ubuntu / Debian

When using Ubuntu or Debian on your VPS this will usually come with a recent version of PHP (depending on the release you are using). Ubuntu 14.04 comes with PHP 5.5 and Ubuntu 16.04 with 7.0 by default. For Debian 7 the default PHP version is 5.4, Debian 8 uses 5.6.

Important!
- It is not without risk to update the PHP version on your VPS. You are advised to always create a snapshot before performing below commands in case something goes wrong.
- The current active version of PHP can be checked by the command php -v via the console (or SSH).
- The steps listed below have no mention of specific PHP 'handlers' or the configuration of your webserver. After updating PHP it is required to restart your webserver (Apache / Nginx) and change things in the configuration (especially when using Debian). To do so, consult the documentation as is supplied by the webserver software.

• Because both Ubuntu and Debian by default do not have the latest version of PHP in their respective repositories, you will need to add an extra repository.
• For Ubuntu:
  you can use the default repository from Ondrej for the latest version of PHP. To do so enter the following command:

  sudo add-apt-repository ppa:ondrej/php

• Should you get an error (that the command is unknown), please enter the following:

  sudo apt-get update
  sudo apt-get install software-properties-common python-software-properties

  After this you can once again enter the 'add-apt-repository' command listed above.
• For Debian:
  you can use the default repository from Dotdeb for the latest version of PHP. To do so enter the following command:

  sudo -s
  echo 'deb http://packages.dotdeb.org jessie all' >> /etc/apt/sources.list
  echo 'deb-src http://packages.dotdeb.org jessie all' >> /etc/apt/sources.list

• After this you can install a newer version of PHP by using the following command (in the example 7.1):

  sudo apt-get install php7.1 php7.1-fpm

• Please note! Above steps will most likely not work (anymore) in Debian 7. In that case you can consult the information listed here for an alternative solution.