Yes, it is possible, but you need to call customer service or go in store to change it.
or advice from an O2 Guru to get through:
If you call 202, when it comes to the reason you are calling stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to someone.
You may have to say "upgrade" to get put through.