You can specify the version of PHP to be used by your site using the "Multi PHP Manager" in your cPanel.
1) Log in to your cPanel
2) Click on "Multi PHP Manager"
3) Tick the box on the same line as the domain for which you'd like to update PHP
4) Select the desired PHP version in the "PHP Version" drop down box on the right hand side
5) Click apply
It can take up to 10 seconds for this change to be applied.