...
You find Instructions for that in the MySQL documentation and in the cpanel forum.
Install PHP5 core
Add the php 5.6 repository, since it is not yet included in Ubuntu
sudo add-apt-repository ppa:ondrej/php5-5.6
If you get an error here, you need to install python-software-properties first (and then do the line above again):
sudo apt-get update
sudo apt-get install python-software-properties
Now Please refresh your package list
...