First download and install the latest BlackBerry Desktop Manager software. You can get it from Here
Install the software so you are up to date on your PC.
Next drill into c:\program files\common files\research in motion\apploader and rename vendor.xml to vendor.old
Next download and install JL Commander on your PC. This will install the application to C:\Program Files\JL_Cmder where you can run JL_Cmder.cmd to start the application. Be sure your Blackberry is plugged in when running JL Commander.
Use JL Commander to wipe the blackberry.
To reinstall the OS on the BlackBerry, connect it to the PC with BlackBerry Desktop Manager installed and you can use the Applications part of the software to update the BlackBerry Software.