Press Y next to the stereo to pick it up then press Y again. When you press Y you will throw the stereo, but it will also change the song it is playing. Also, stereos can all be playing different songs; you can change the song on one and it will not change the others. There are a total of four songs that can be played.
This can be done during both days. Go down the stairs to the parking lot and look at the building that reads "Fayju"(across from frog court building). While looking at it, two of the windows are white. Use the trampoline in the parking lot to launch your frog at the white area. Instead of smashing into a wall, you will land in a completely white room. The room is game creator Fajyu's office with its window view.
Get to the area with the bouncy castle. While looking at the castle from the front, look left and go to the trampoline. Use the trampoline to get on top of the white building next to the one that reads "Frozies Swindon Hotel". When on top the white building, run towards the other white building behind the Frozies Hotel and you should fall outside the map. To get back in, run through the building you were just on the parking garage wall.