Which version of the Xoom do you have? Motorola have so far only released an ICS update for the US Wifi version of the Xoom (the 3G version and the International version use different firmware and haven't had the update yet, applying this update to those models may harm them).
If you do have a US Wifi Xoom then Motorola are already actively pushing this update out and have been doing this in batches since 24th Jan. If your device is regularly connected to the internet and hasn't automatically picked up the update yet, then you can force it to go and check by going into Settings -> About tablet and selecting System updates it should then go and check for you.
In the future, if you want to have a chance of getting Xoom updates early, you can join the official Motorola Feedback Network, members of that group did reportedly get the ICS update a few weeks earlier than everyone else. Join it by signing up at the Motorola Forums and selecting the "Motorola Feedback Network" option.
If you do want to do this manual update, then you can pick up a USB OTG (aka Host Mode USB cable) very cheaply on eBay, I got one for connecting my camera to the Xoom for a couple of pounds, including postage from Hong Kong!