Go to the hardware store and buy a few 5-gallon buckets. Transfer your rock to the buckets, and pour enough water in to keep them wet. Once all the rock is removed, it will be easier to catch your fish. Move your fish into the other buckets (keeping them wet, of course!)
Then drain the rest of your water (try to save as much of it as possible), and scoop your sand out into the new tank. Add the water back in, add the rocks back in, and let it settle for an hour or so (it will be cloudy). Then put your fish back. Voila!