Ubuntu does not include PHP 5.6 in its repository. In order to upgrade from PHP 5.5.x then please follow this guide.
Step 1
Add PHP 5.6 PPA to the local repository database.
Step 2
Update the server repository database.
Step 3
Install PHP 5.6
Step 1
Add PHP 5.6 PPA to the local repository database.
Step 2
Update the server repository database.
Step 3
Install PHP 5.6