I had received the following email about the same topic. I just called their tech support team, who tested it for me and completed the upgrade process. My website has been running fine.:
PHP, the web programming language, has several different versions and we will be phasing out PHP version 5.2 in the near future as it has been unsupported by its creators for several years now, along with PHP 5.3. You are receiving this email because your account was found to be using php version 5.2/5.3.
If you're not certain of your sites compatibility with PHP 5.4, you can quickly and easily test it by changing your account to PHP 5.4 single using the outlined steps below. If, after changing your PHP version to 5.4 and your site looks normal and operates without any errors then your site is compatible. If you update to PHP 5.4 and you find your site showing errors or a blank white screen that is a good sign that something in your site is not compatible. Most commonly these are plug-ins or themes that need to be updated. Switch the PHP version back to 5.2 or 5.3 and login to your admin panel and check for any available updates. If none are available you will need to check with the plug-ins/theme developer to see if they have compatibility with PHP 5.4.
It is strongly encouraged you check yours sites plug-ins/themes/3rd party scripts for any updates in the next 7 days to avoid any downtime or issues with this process.
If you do not then your account will be automatically upgraded to 5.4 along with any extensions you have chosen to include in your current 5.2/5.3 configuration.
You can upgrade PHP by:
1. Navigate to your cPanel
2. Go to the Category Software/Services
3. Click on PHP Config
4. Scroll down and select any of the PHP 5.4 options and save
We also have 2 great guides that explain the difference between all the PHP versions.
For support go to http://helpdesk.bluehost.com/
Toll-Free: (888) 401-4678