If you want to take advantage of the new awesomeness, you can do so very easily thanks to a PPA.
If you've never added a PPA before, you will want to make sure that you have
python-software-properties installed so you have the command available. To install it, you just need to run:
$ sudo apt-get update && sudo apt-get install python-software-properties
Note that Tested on 13.10 as the comments below indicated, this may also be necessary:
$ sudo apt-get install software-properties-common
Once that's installed we can add the new PPA:
$ sudo add-apt-repository ppa:ondrej/php5-5.6
After the PPA is added you will need to update and upgrade. This will upgrade your current version of PHP to 5.6 along with any modules you have installed:
$ sudo apt-get update && sudo apt-get upgrade
If you don't happen to have PHP installed already, you can do so now and you will be installing the latest and greatest:
$ sudo apt-get install php5
You can check current installed PHP version use this command:
$ php -v
Once this is done, you will want to restart your web server software and/or fast process manager.