If you want to upgrade your PHP 5.3 to PHP 5.6 running on Ubuntu 12.04 with nginx, you need to follow these steps :
Step 1: Add the PPA repository for PHP 5.6
sudo add-apt-repository ppa:ondrej/php
If you are logged in as the root user, you can leave out ‘sudo’ from the above command
If you see an error like this :
sudo: add-apt-repository: command not found
this means that you need to install the package python-software-properties
sudo apt-get install python-software-properties
Now run the first command, to add the PPA again.
Step 2: Install PHP 5.6 to your server, but before that, backup your php.ini file
cp /etc/php5/fpm/php.ini /etc/php5/fpm/php-backup.ini
Now we install PHP 5.6, along with the most common packages required for WordPress sites with Nginx.
sudo apt-get update sudo apt-get install php5.6-cli php5.6-common php5.6 php5.6-mysql php5.6-fpm php5.6-curl php5.6-gd php5.6-soap php5.6-mbstring php5.6-zip php5.6-mcrypt php5.6-xml
You might be asked, if you wish to replace the current php.ini file with a new one. Select yes for that and replace your existing php.ini with the new one.
You can update the changes you had made in the previous php.ini file to the new one, by comparing it with the php-backup.ini file