You need a 1/2 inch drive socket with a 10 mm hex (Allen head) protruding from the end of the socket. Or you can take a 10 mm allen wrench and cut about 2 inches off of it (use grinding wheel) and insert the cut off piece into a 10 mm socket with i/2 inch drive.
Turn steering wheel all the way to the left in unlocked position and then using the socket, extension and breaker bar (not the rachet) remove the nut. Allign steering wheel to level position and remove it.
Regarding tightening, use the German generic tourque of Goodntight.