This firmware release is specifically for users in Singapore:
Warning: Do note that this is a wipe rom. It means that it formats /cache , /data and /HWUserData. So do your necessary backups before proceeding with the flashing.
The flashing instructions are included in each of the firmware packages. The ICS ROM flashing requires you to have a microSD card (at least 1GB in size) to store the firmware for upgrade. The upgrade is straight forward but do note (again) that it actually wipes off your user and application data. So do any necessary backups prior to the upgrade.