Making sure that your PHP version is up to date and not running a legacy version that is no longer supported is important on many levels.
Having an up to date PHP version allows you to take advantage of speed optimisation, security improvements and new features that come with later versions.
By default, most SiteGround servers come with the last version of PHP 5.3.x which is 5.3.29 and on a lot of Joomla websites this should be upgraded further to the latest PHP 5.5.x.
It's a quick and easy change in the .htaccess file that you can find our your SiteGround server or SiteGround cPanel account.
Login into your cPanel account and look for the file manager.
A popup will appear, make sure you choose "Show Hidden Files"
A list of files will appear showing your website files for Joomla. Navigate to the /public-html/ folder. You should see a file called .htaccess. This will only appear if you selected "Show Hidden Files" in the previous screen.
Select the file and click on Code Editor in the toolbar of your file manager to open up the contents of the file.
At the top of this file add this line of code:
AddHandler application/x-httpd-php55 .php .php5 .php4 .php3
This will set your website to use PHP 5.5.x. The latest version that SiteGround has of the 5.5 series.
You can also change it so something event later such as 5.7 when that is released (Currently not released at the time of writing this article).
Click Save and test your website.
Make sure it is still working as it should. If it isn't working, remove the line of code that you just added.
Also as a secondary note, please make sure you backup your website before attempting to do anything to your website.
The team at SiteGround will help you out with any of this if it is too hard or goes over your head.