1. Make backup of BB
2. Wipe with JL_Cmder
3. Download and install the OS package to the PC.
4. Delete vendor.xml file located in c:\program files\common files\research in motion\apploader
5. Plug in BB, open Desktop Manager and run Application Loader and follow the prompts to load the OS back to the device. (it's normal for the hourglass to spin for up to 20 minutes on the first reboot after the device software is reloaded.)
6. Restore the backup file.
Check the sticky thread for more info. The only extra step you are doing is the wipe and manual restore. Usually, during a normal upgrade the Desktop Manager will backup and restore automatically. You are simply going to do it manually because you are cleaning the device and loading the OS fresh.