Repair or delete? Huh?? Can't recall seeing that..
There are two components: Desktop Manager, which I assume you have installed, and the handheld OS. Desktop Manager can be downloaded from the RIM BlackBerry support web site.
The locations for all of the downloads can be found at BlackBerryOS 4.x Download FAQ - UPGRADE DOWNLOADS
Download the latest handheld OS for you BB
Execute the downloaded program
Locate and delete VENDOR.XML from your PC C: drive
Start Desktop Manager
It should scan your BB and attempt to update it.
Not sure what is going wrong.