There is a new ICS update that will bring your phone to version 4.0.4. You can get it through Kies. If you don't have Kies installed, get it here
Beginning August 16, the Samsung Galaxy S II (ICS only) will have a software update to Android version 4.0.3 / Software T989UVLH1 via Samsung Kies only. This update improves device performance.
You can update in one way:
Manual download to T989UVLH1: If you want to update to T989UVLH1, you can update via Samsung Kies. Ensure you are on the latest version of Kies prior to attempting the update. See Kies - Sync Media, Contacts & Calendars Across All Devices | Samsung to confirm the version.
Current Software VersionUpdate StatusT989UVLH1
Android version 4.0.3/ Software version T989UVLH1 - Current optional update version
T-Mobile Support Docs
- Android version 4.0.3/ Software version T989UVLH1
- Manual Update ONLY (Size varies based on previous software version)
- Approved 8/14/12
- ISIS/NFC update
- Bug fixes
- Android version 4.0.3/ Software version T989UVLE1 update
- Latest version of Kies software downloaded on PC or MAC
- At least 50% battery life
I know that says 4.0.3, but as you can see it is 4.0.4
After updating, I highly recommend doing a factory reset. It will cure most of the problems you might encounter after any update.