First and most important thing is that you MUST do full flash (this is the best way)with MAIN,FS and CUSTPACK according to your phone status (depends on CID in your phone) and files you will find here Top Sony - Download and if you wont free download read this How to get access to Download Area? - Top Sony Forums or you can buy PREMIUM account on this site.

To be sure what firmware you need post log from XS++ here and we help you