using a USB cable. A complete set of directions can be found at the sourcelink, and when you're done your Samsung Galaxy S II will be running Android 4.0.4.
Among the new features will be Face Unlock which allows you to unlock the phone using nothing more than your face, updated icons in the pull-down Notifications screen, a more intuitive interface, and new pre-loaded apps like Slacker Radio and Google Play Movies and T.V. The update also offers improved text input and editing making it easier to copy and paste, and edit. New options support encryption in the phone and on a microSD card if you're using one.
source: Samsung, U.S.Cellular via AndroidCentral