You are going to want to use as much of your existing sand, water, rock etc as possible in order to retain your biological system. If you will need additional sand to cover the bottom of the new tank, I would put that in first as mentioned earlier, add about 1/2 tank of new salt mix with the heater now turned on. move as much of your water as you can over to the new tank and top off the old tank with fresh salt water as if you were doing a water change. I would go ahead and move all the live rock over once the water temperature is up in the new tank. You may not even go through a cycle this way at all and may be able to move your fish over as soon as the sediment settles down and all is running well in the tank. OH, y es and use all of your existing sand. There are all kinds of organisms there you want to preserve. If you want to clean it, siphon off some of the existing tank water (I do hope you have a few large rubber trash cans to do all this!)
and just rinse your sand briefly in this before placing it in the new tank. You want to disturb your existing tank as little as possible, but it is going to get cloudy once you start moving things. Have fun!