By default your server will always run the oldest stable version of php that is still supported (not yet end of life) . This is to insure maximum compatibility with the widest range of legacy scripting. If your script requires a newer version of PHP you can update the php version to the next stable branch by using the PHP Multi Select icon in your cpanel under the Programming Section.
Select the domain using the checkbox and the version you wish to run then click the apply button. This will modify your .htaccess file to add a new php directive to instruct your scripting to use the php version you have chosen.
If running the newer version of php causes an issue with your script you can revert it back using the same procedure.