You will have to find a temporary place to put the corals and fish and rock. Rubbermade trashcans and tubs are great for this. If you take the sand out and put it in the empty new tank then you can limit the cloudyness by adding the saltwater into the tank by pouring it into a bowl that is placed on the sand bed or using a pump to pump the water into the new tank and pumping it into a bowl so as to not stir up the sand. Once you have the tank about 1/2 full of water then you can add your live rock back to the new tank and then continue to fill the tank till its 3/4 full or so and then add your corals and fish back to the system. Make sure all your plumbing is set and ready and then finish filling the tank and start up your pumps, etc.
Use as much water from the old tank as possible but you will have to mix up some new saltwater to make up the difference. Mix up this new saltwater prior to the change and have it up to tank temperature to help minimize the stress.
