However, if you are running a rooted version of ICS, you'll need to follow this guide to download the update and install by booting into recovery.
The 4.0.4 enhancements include:
- Quicker screen rotation
- Ability to immediately lock the tablet with the power button
- Microsoft Exchange improvements with additional EAS policies
- Better phone number recognition
- Camera and image quality improvements
- Improved stability
Summary from XDA
This is a modded update package (update.zip) that updates the US Xoom Wi-Fi from any ROM to stock rooted Android 4.0.4 IMM76 using ClockworkMod Recovery:When installing it remember to copy the update ZIP file to your microSD card and install it from there otherwise it will appear to install but when you boot your system it will be on the same version.
- Flashes bootloader from a previous update (3.2.1 HTK55D) to ensure integrity (bootloader remains unlocked)
- Flashes the boot partition with rooted stock 4.0.4 boot image, stock kernel
- Stock ICS update fixed the Bluetooth tethering issue that was introduced in 3.2
- Stock kernel includes no extras (overclocking, etc.) from custom kernels
- Flashes system partition with rooted stock 4.0.4 image (minus the recovery overwrite script; includes gapps)
- Includes Superuser.apk 3.0.7 and su binary to enable functioning root (thanks, chainsdd)
- Hardware SDCard continues to be read-only via documented application permissions
- Leaves existing recovery partition intact (unmodded stock 4.0.4 update overwrites it on every reboot)
- Leaves user data intact (note: some users updating from custom ROM's recommend wiping data/factory reset to prevent issues)
I installed this on my Xoom and all of my data was intact but you should backup your data just in case.