You can download the update directly on your iPhone, iPad or iPod Touch through the Apple App Store or by using the link which follows:
Facebook for iOS version 5.5 has the following new features and improvements
- New button design makes it easy to like, comment and share posts in News Feed.
- Improved buttons to like, comment and share posts make the process more streamlined.
- Share button to re-post stories from your News Feed now available in all languages.
- Call friends for free right from Facebook as you would on Skype (US and Canada). Keep in mind that you will require a data plan in order to take advantage of this service