Most crystal chandeliers require that you unscrew the bottom in order to remove the arms. Ours are no exception. It is also good to remove the bottom when doing a deep clean - you can clean in between the metal and the crystal bowl and perform maintenance, making sure everything is tight.
For extra safety, place a heavy quilt or comforter on your table or floor beneath the chandelier and cut the power to the chandelier before you start working. Remove the prisms from the bottom and lay aside.
The bottom should have been installed in one piece - meaning the metal bowl, 2 crystal bowls and finial are all locked together and screw onto the bottom of the chandelier as one unit.
Ideally, when you turn the bottom, it will all unscrew. IT IS VERY IMPORTANT that you do this carefully and with a good grip on the bottom. When the threads run out, the bottom will drop into your hand, and you want to be prepared so that it does not fall out of your hands. (On our chandeliers, the metal plate is fixed to the pipe - it will not unscrew.). MAKE SURE that the whole chandelier is not turning or you may turn it out of the ceiling!
If the bottom on your chandelier is not unscrewing, make sure that you see the metal bowl turning. You may have to reach in and grip that to turn it as well. Do not cut yourself here. Those metal edges may be sharper than you expect.
If the bottom is still not turning, you may have to remove it piece by piece. Start by removing the finial and working up. HOWEVER, be very careful here - you don't want the pieces to start dropping. Always have your hand on the next piece to be removed.
These instructions are general. Keep in mind that chandeliers are built by hand and installed by human beings and are all different. What works for one may not work for another.
Here you can see how the arms are held onto the plate by a hexagon nut and washer.