Do you mean the vendor xml file?
Deleting the vendor xml file is only for if you are upgrading your BlackBerry's software and using one from another carrier, for example putting a Verizon 8130 software package on an Alltel 8130. It is not something you find on the phone itself, but in the apploader file of the software/OS package that you would download to your PC. Once downloaded it can be found in C:\Program Files\Common Files\Research In Motion\AppLoader
Upgrading to a newer version is best from your own carrier, however sometimes issues with your device can be helped by an upgrade and if none is available from your carrier then a newer one from another carrier may do the trick. This is when deleting the vendor xml is needed.
Here are a couple of threads that talk about upgrading and what the newest device OS/Software packages are:
Hope this helps, if not, just post back and someone will try to help you out