How to upgrade Blackberry OS

Upgrading sometimes is required as I did to get OS 5.0 from my previous OS 4.7.1, many things were improve with the higher OS but doing on Blackberry is little bit difficult and risky. So if you're insisted, then "Do it with your own risk !!!". Some 3rd party application or themes may not work with different OS.

Preparation :

1. Blackberry Desktop Manager. Download here
2. Device Software. Download here. Select base on your carrier/provider and your BB type and choose what version you want to install on/upgrade to.

Upgrading :

1. Install BB Desktop Manager
2. Install your new device software, once completed find folder (C:\Program Files\Common Files\Research In Motion\AppLoader), get and delete file name vendor.xml .
3. Launch BB DeskMan, connect your BB via USB cable, if App update prompted, select cancel.
4. Backup your data from option Backup and Restore menu, this will only save your contact, profile setting, menu icon arrangement, etc. If necessary backup also your 3rd party applications.
5. Select Application Loader from BB DeskMan. Check at all important app and uncheck which is not necessary or just let it as default.
6. Choose "Do not automatically back up and restore the device application data during the loading process", click Next and Finish. Upgrading will be started and take 30-60 minutes or more. DO NOT DISCONNECT YOUR CABLE OR SWITCH OFF YOUR PC it could break your handheld. 
7. Once Process completed it will boot your BB automatically.
8. Now your BB should have new OS and don't forget to restore your data and 3rd party app.