Sprint is updating the Samsung Galaxy S II Android 4.1 Jelly Bean. This is good sign to Samsung Galaxy S II owners on other carriers, that usually follow with updates soon after.
The update must be completed using either the Kies app or Samsung's Simple upgrade tools. You will not be able to make emergency calls during the update processes. Don't stop the update once it starts. Don't forget it is always a good idea to backup your data before and update as well as have your phone fully or at least 50% charged during the update.