How do I upgrade PHP version to the latest stable released version?

I'm using a system running on Ubuntu 12.04 LTS 64-bit OS.

I'm currently using following PHP version on this machine:

Command used to get the below info at terminal : php -v

Details I got are as below :

PHP 5.5.19-1+deb.sury.org~precise+1 (cli) (built: Nov 19 2014 19:32:34) 
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2014 Zend Technologies
    with Zend OPcache v7.0.4-dev, Copyright (c) 1999-2014, by Zend Technologies

Now I want to upgrade my PHP software to version 5.5.20.

Before asking the question I tried following command:

sudo apt-get update

Some information appeared. Then I again hit the following command:

php -v

but still the PHP software didn't update.

How should I do this?

apt-get update updates only the package lists. To actually upgrade the packages you have to run:

sudo apt-get upgrade

or

sudo apt-get dist-upgrade

More info here.

If you ran the above commands but the packages still were not upgraded, probably you didn't add Ondřej Surý's PHP PPA to your system.

Run the following to add the PPA:

• For PHP 5.5, PHP 5.6 and PHP 7.0:

  sudo apt-add-repository ppa:ondrej/php
  

• For PHP 5.4 (Deprecated, upgrade at least to PHP 5.5):

  sudo apt-add-repository ppa:ondrej/php5-oldstable
  

• For PHP 5.5 (Deprecated, use ppa:ondrej/php):

  sudo apt-add-repository ppa:ondrej/php5
  

• For PHP 5.6 (Deprecated, use ppa:ondrej/php):

  sudo apt-add-repository ppa:ondrej/php5-5.6
  

Then update the package lists and perform the upgrade:

sudo apt-get update

For PHP 5.5:

sudo apt-get install php5.5

For PHP 5.6:

sudo apt-get install php5.6

For PHP 7:

sudo apt-get install php7.0

Release upgrade

If you want to install the latest PHP (for example PHP7) but you want to stick to the release's packages intead of hacking the sources around; and you want to do a full-release upgrade (for example you are in Ubuntu 14.04 -which does not have php7- and you want to go to Ubuntu 16.04 -which does- then you can do:

do-release-upgrade

Now you should have the latest PHP version.

For newest updating process use the following command

sudo LC_ALL=C.UTF-8 add-apt-repository ppa:ondrej/php

Then run the following command in terminal

sudo apt-get update 

This is worked well when installing php 5.5,5.6 and 7.0

If there some errors this command will resolve the errors

sudo dpkg --configure -a

Update 2020-10-14: For versions upto 7.*

sudo apt install software-properties-common
sudo add-apt-repository ppa:ondrej/php
sudo apt update

Then

sudo apt install php7.2

Here also you can use this for php 7.0,7.1,7.3 to 7.4

After updating process you can use below command to install extensions

sudo apt update 
sudo apt install php-xml

or you can use like below

sudo apt install php7.2 php-xml  

Update 2021-01-31: For versions upto 8.*

sudo apt-add-repository ppa:ondrej/php
sudo apt update

Then

sudo apt install -y php8.0 php8.0-cli php8.0-common

Run the following to add the PPA:

sudo apt-add-repository ppa:ondrej/php5

By upgrading PHP from version 5.3 to 5.5, this may upgrade your Apache from version 2.2 to 2.4. So be careful.

If you want to upgrade only PHP 5.3 to 5.5 and do not want to upgrade the system, then you need to install apache 2.4 as well.

sudo apt-add-repository ppa:ondrej/apache2 -y
sudo add-apt-repository ppa:ondrej/php -y
sudo aptitude update
sudo apt-get install apache2 libapache2-mod-php5 

Beware about some changes in apache 2.4 related to require grant all.

https://httpd.apache.org/docs/current/upgrading.html

On Ubuntu 14

Only this line is needed

sudo apt-add-repository ppa:ondrej/php5-5.6

Then

sudo apt-get install php5

This will trigger the PPA upgrade system