Nokia Belle

Nokia Belle is the new Symbian OS from Nokia. It is available in new phones and also existing users can update their phone to this OS.
As of now the Nokia Belle update is available only for the following models.
Nokia N8, Nokia E7, Nokia E6, Nokia C7, Nokia C6-01, Nokia X7, Nokia Oro or Nokia 500

How to update your phone to Belle os ?

Step 1 : Connect Your Nokia phone with pc via Nokia Ovi suite(Nokia Suite 3.3 is required)

Step 2 : Go to tools menu and select software updates, Download will be started

The interface also includes new features like imaging applications with HD video recording at 30 frames per second and a visually improved browser enabling enhanced browsing and viewing of Web videos. The menus have been simplified and a notifications bar has been added to make accessing key settings or features faster. In addition, with Belle users can also boost productivity on the go with a wider selection of Microsoft Apps, such as Lync and OneNote that will soon be available for free download on top of Belle.

You can find whether the update is available for you by checking the following link..
nokia-belle-update

Official Belle Site.
Nokia Belle

According to the official site the following are the cool features of the new OS update.

Faster and smoother browsing
Share & pair with NFC
Live widgets in five different sizes
Pull-down task bar

Disclaimer: I am not responsible if anything happened to the phone after the update..... :)