Changing the OS

[stuckupvacant1]

Hello Guys, newbie here
Just got my first BB (2nd hand mind you)

So my question is how can I change my OS?

I've read this FAQ
blackberryfaq.com/index How do I upgrade the OS on my BlackBerry? -

but's that's to upgrade it

I want to change it from uk vodafone to uk o2
(i know i could just unlock it but i want to completely change it)

I've downloaded the lastest o2 desktop manager and installed it
Deleted the vendor.xml file from the common files folder

Yet it doesn't seemed to have worked

Is there a helpfile for removing one OS and loading a new one?