If you are kind of use who loves to hacked or leaked version or taking one step head try installing stuff which might just brick your BlackBerry, RIM has complete set of instructions online to bring it back.
What you need :
- Internet Connection.
- BlackBerry Desktop manager.
- And a USB connector.
One this is set just follow the instructions for PC users and Mac Users. You will have load the Operating System again by using the update feature and select correct language.
It will install the core applications but rest of your application and data will be lost. If you have made backup of your blackberry you can get them too.
Related : How to update BlackBerry Device Software