A written version of this guide can be found here:
instructions on the differences in PHP versions can be found here:
If your website currently uses PHP you can upgrade to the most recent version within your control panel. Should your website experience any issues following the scripting language changes, you can downgrade back to your current version.
It is your responsibility to ensure that your website is compatible with your selected version of PHP. Fasthosts cannot provide any support for the scripts that are in use on your site.