PHP is a server-side scripting language designed for web development but also used as a general-purpose programming language
Before upgrading your PHP version from 5.2 to 5.4 you should make sure that your blogs WordPress version is up to date and all your themes and plugins are also updated to their latest version so that you won't face any problems or downtime. After making sure that all the things in your WordPress blog are up to date then follow the below steps to update PHP 5.2 to 5.4
First of all Login to your hosting account.
After logging in now navigate to your Cpanel in Bluehost account.
Now go to the category Software/Services
Now click on PHP Config.
Now you will see a list of PHP versions just choose PHP 5.4 version and click on save changes.
After saving changes now move to your site and see that everything is working fine if you find something mishappening with your site then follow the steps mention above from step 1 to 4 in 5th step choose 5.2 again and then try finding out which version are incompatible with PHP 5.4 and if they are not much important then try removing them or find an alternative.