How is this urgent?
Anyway, here's what you do:
1. Download the os you want to install.
2. Locate and delete the vendor.xml file. Best best on a windows pc is to press windows key+f and search for vendor.xml. Then delete it.
3. Attach BB to the pc with the usb cable, open the dekstop manager and run the application loader.
4. Follow the instructions on the screen.