I am not sure I understand the question..what is an AO image?
You can open the 512 x 512 image. Then resize the canvas to 1024 x 1024. Then duplicate the layer 3 times so you have four layers each with the same 512 x 512 image. Now using the move tool align the images. You will probably need to zoom. Then under the image drop down menu select merge visible layers.
edit: oops, Ofnuts is more experienced than I. His is a better solution than mine.
You can open the 512 x 512 image. Then resize the canvas to 1024 x 1024. Then duplicate the layer 3 times so you have four layers each with the same 512 x 512 image. Now using the move tool align the images. You will probably need to zoom. Then under the image drop down menu select merge visible layers.
edit: oops, Ofnuts is more experienced than I. His is a better solution than mine.