If you look underneath at the transfer casing you really cant miss it. Its not covered up by the bottom shield or whatever its called, so there is no need to remove anything. It a small motor about 6 inches long and should have a cable going to it with a big plug. Disconnecting it stops the xdrive system sending any power through the transfer box (by magic, no idea how it works!).
I unplugged mine because i have a serious wobble issue that nobody in the omniverse seems to be able to cure without me spending thousands! no drive to front wheels equals no wobble. Happy days! Although i do need to plug it back in and put up with it when it snows......