Here's a quick tutorial on how to upgrade you XAMPP installation to use latest version of PHP that is PHP version 5.4.
1. Download windows build from the official site. ( I had used this link.)
2. Extract all files from the downloaded archive to a temporary folder say php_new.
3. Make sure XAMPP / Apache is not running.
3. Go to the folder where XAMPP is installed and rename the folder XAMPP_ROOT/php to php_old
4. Now go back to our temporary folder i.e. php_new and copy all files to XAMPP_ROOT/php where XAMPP_ROOT is obviously the folder where XAMPP has been installed.
5. Enter the php folder and locate the file(s) php5apache*.dll ( Example php5apache2_2.dll )
6. Copy those files to XAMPP_ROOT/apache/modules/ depending on your version of Apache
7. Optionally delete the folders php_new and php_old
8. Start Apache again and verify that everything is working smoothly by creating a phpinfo file.
9. Don't forget to rename php.ini-production to php.ini and edit it as per your needs. ( Example: set extension_dir to XAMPP_ROOT/php/ext
10. Check Apache logs for any possible errors.