Suggestions on PHP upgrade

We are currently using Drupal 6 with PHP 5.3.0 and we found there are few vulnerability found in PHP.I this case, do we need to update the version again? or do we get any fix for these vulnerabilities?

System details

OS: Red Hat 3.4.6-3 (Red Hat Linux AS 4.5)
PHP Version: 5.3.0
mySQL: 5.1
Drupal: 6.x

and Is it required to update the PHP frequently?
How can we install the fix for PHP versions?

You should upgrade to 5.3.8. Generally, you should upgrade when the version of your server has vulnerabilities.