The M93 has an integral tube.
-Undo the lock nut on the receiver extension, use the proper tool, if not available, a strap wrench will do.
-When the lock nut is loose the receiver end plate will be able to rotate with the extension, it is holding in the takedown pin detent spring, so like gunslinger said, make sure you don't lose it.
-Unscrew the extension tube from the receiver, put your thumb on the buffer retainer as the receiver extension comes out, or else you will launch it.
-That's it.