If there is a firmware update you should be able to do it 'over-the-air' on WiFi using the settings... you can check (somewhere in the menu) for updates, this should tell you if your phone is up to date.
Alternatively, post your version numbers and I'm sure someone can tell you if it's up-to-date.
Is your phone 'locked' to O2 or is it de-branded and open to all networks? Sometimes Operators can release their own versions of phones firmware which may differ from that of other networks or open phones.