You have to keep making matches of 4 or more tiles simultaneously over and over until the powerup becomes the fireball and then use it on the center tile at the very bottom of the puzzle. There is an element of speed required to get this to happen. Then repeat the process of charging the powerup back to the fireball again by making large matches over and over in the top half of the puzzle and use the fireball again on the same spot at the bottom. Do this a total of 3 times and all the pieces in the bottom should drop out together. Use the hammer on the two pieces in the top section if they have not fallen out on their own or you weren't able to shuffle them down into the corners to drop them out.

Some players only use the fireball twice and then shuffle the tiles around in the bottom section if there are easy matches available to drop a few pieces, then use the hammer to get the rest. Good luck!