[Statman]

Here is what I did:
1. Download 4.5.0.135 OS to your PC
2. Install/run OS to PC
3. Delete vendor.xml file. It's located in c:\program files\common files\research in motion\apploader
4. Click loader.exe (in the same folder as the vendor file) and that will start the process. It will go through a number of steps from backing up your BB to installing OS to installing third party, to installing preferences. The BB will re-start multiple times during this process. Just be patient and let it do its thing.
5. Do not unplug BB during the process. It will take around 30-60 minutes to complete upgrade (took me 23 minutes).