Default PLS Help me :)

Hey guys,

my sister have a HTC 7 PRO
with 7.0.7392.0
and firmwareversion: 2250.10.12401.207.

she bought a prepaidcard from vodafone, and the dataconnection didnt work.
Vodafone said, that the phone can have a o2 branding, so vodafone can not connect to internet with that phone.

Can anybody give me an indrodution step by step, what i should do?
-Downgrade and root and unlock and delete o2branding?

pls help me ... thanks a lot