The three Galaxy S II variants in the US have yet to receive the Android 4.0 ICS upgrade but the unlocked version is going to be the first to get it. An OTA update was pushed out today and will allow you to update your device to the newest version of the operating system.
The update comes in a 126MB package, and will wipe your settings for music playlist, Homescreens, APN, and other things so make sure you have everything backed up that you want to keep. The download shouldn’t take too long depending on the connection you have and you can use the phone while downloading the update.
If you have not yet received the notification about the update you can check manually in the settings.