Hello, there are many different forums containing all the info you need, www.google.co.uk will find you all you need to know.
Nokia Service Suite aka NSS, is the tool you use to read and change the product code.
Then you need to find out the product code you want.
My current Firmware version is v. 4.0839.42.0.1, it is unbranded (no more Orange firmware), i dont know if i am allowed to post product codes here or not, but here is mine anyway, 0529803. Use this if you wish or seek your own.
There are different types of firmwares, they are called APAC (Asian Pacific and China) and EMEA (Europe, the Middle East and Africa), this is mostly for defining language packs and whether or not they are ME or IE versions (Music Edition and Internet Edition).
Once you have learned how to change your product code, you can then connect your phone to your PC, download and install the latest Nokia Software Updater program for your PC found at Nokia's website, free!
Make sure you follow all instructions, make sure your phone is fully charged with a SIM card inserted and set to General Profile and be sure to keep the phone and cable in a place where it cannot be knocked or snagged, a disconnection of the data cable could mean a bricked phone.
This is just a brief outline, firmware updating on Nokia phones is not a new thing anymore, there are many forums full of the right info (and wrong info too).
I have updated my phone many times now, but be warned, once you have updated, theres no going back to your original firmware without flashing the phone.
Good Luck
Regards
Markkyboy