To able to Ugrade to ICE BEAN Android 4.1 ( Jelly Bean )
 you have flash new Kernel below or Update to latest System from OTA 
Working On:
Doomkernel ICS
Sony's ICS Kernel
Arcknight
Xarc
SeGA
Recomnend:
Xperia arc S + Arknight 3.X + a Working Brain
System Information
Base: ICS 4.0.4 @4.1.B.5.8.7
Fully Zipaligned, Deodexed, BusyBox, Superuser & Binary
100% Bloatware Removed
Clean Database, Fix Emissions @Boot
Supercharged services.jar
Supercharged
ICS with Xperia S & GX + JellyBean Apps
build.prop fully tweaked
hw_config optimized
xMoD Hosts by Adaway (No Ads - Never Again see Ads @XDA App)
JellyBean UI Sounds AOSP
Xperia + Nexus Bootanim
System Apps
Xperia S Settings
Album App by Xperia GX
Themed Walkman App by Xperia S
Holo Themed MooDeD Camera
Xperia S Phone & Contacts
JellyBean Google Play
Xperia S KeyBoard
Xperia S Launcher
Xperia NXT Widgets
Xperia S Messaging App
Xperia S Calculator
Xperia GX with JellyBean Transparent White Font Statusbar
Xperia S Notes
Xperia GX Calendar
Xperia GX Album




Installation Instruction
This ROM works on Locked and Unlocked Bootloaders. Its a Flashable ROM.
0. Charge Phone 100% (optional)
1. Flash Kernel for ICS ROMS (e.x. arcknight)
2. Boot to CWM
3. Factory Reset
4. Mounts & Storage ---> Format System
5. Advanced ----> Wipe Battery Stats (optional)
6. Install Zip from sd card ----> Choose Zip from sd card ----> Xperia Ice Bean 4.X
7. Reboot, wait for booting, than reboot again (optional)
Youtube
Original link from : XDA