Altered Corpse said:
If it's in warranty a Nokia service centre will do it for free.
Not necessarily. As a service centre they can only upgrade you to the next approved firmware for your network provider. If you want them to do anything else (eg update an Orange handset to the latest unbranded firmware) then it's not a warranty issue (and in fact most service centres won't touch such things at all because it puts their SC contract at risk)
To those earlier in the thread, it's also worth noting that the main reason people notice their phone speeding up after a firmware update is nothing to do with the firmware, and everything to do with formatting and defragmentation of the file system as part of the update. You can just format the phone to get those gains.
It's rather akin to formatting your C drive and installing a fresh copy of windows, then installing a new update and claiming it's magically become faster than the 2 year old install you had previously.