May also be good to point out the before embarking on any flashing remember to make a back up of your GDFS, as this is specific to your phone and if you lose it, or you corrupt ur gdfs and you havent made a back up then you will end up with a "BRICK", or a paper weight!!
You can do this through Setools and just click read gdfs, this will make a backup in your setools folder.
Also if you arnt very confident you might just be as well to try and update your Firmware/software first through the SE update service (SEUS). If your firmware/software is old this will update it to the most recent one for your handset. If this doesnt get you anywhere then im sure you will be able to download the correct upto date MAIN, FS and custom files from the download section on this site. Just make sure that you correctly ID your region, ie Europe, Asia, US and region numbers etc so you are certain you have downloaded the correct files as these are also specific to your country.
There are tutorials at the top of the main forum section that tell you step by step how to flash your handset easily.
Hope this helps
Lav