To Warp to World 4 you must be in World 1-2. When you get to the moving platforms jump onto the platform. While on the platform get a running start then jump to the to the small brick ceiling then jump again to the next brick ceiling. Keep going until you see 2 pipes. Go down the pipe that's on the far left. You will be led to a secret area with lava. Make sure that Mario or Luigi is small. Run under the small lava pit that's positioned under a brick wall. After you make it under the lava pit keep going until you see a pipe. Don't go down the pipe. Instead, search for a secret coin block that's located one space to the left of the lava pit. Then get on the coin block and look for a coin block that's located one space to the right of the coin block that you are on. Jump on next coin block and jump up to brick wall ceiling. You should find a Warp Zone that leads to World 4.