Ok, click this link and select which phone you have and follow the instructions.

http://www.nokia.co.uk/A4226014

This link will tell you if you have any available updates.

http://www.nokia.co.uk/A4305060

You will need to download the program to run on your PC and that will guide you through software updates. You will need the PC data cable and a fully charged battery or the phone at least to be on charge.

SMS accelerator can be found here if you haven't got it.

http://europe.nokia.com/A4149142