Okay, i did this restaurant menu on n73.. I've shrinked the image files to it's minimum, and the memory panel in device central shows a graph that is nearly full.. whenever i exceed it, it will turn my graphics into red boxes.. how can i clear those things in the memory? and i still dont know how does this memory actually works..

So whenever i put new graphics into the artboard, it will use up more and more memory and i will never be able to finish this assignments if its like this.. Can anyone help me??