i suggest to use .paaplug for photoshop, so you can save it directly to paa.
The only important thing, it must be a n^2 number for the size, e.g.
16x16
32x32
256x256
1024x1024
if you use that plugin you dont have to modifiy anything just save it.. only if you got a some invisible stuff (alpha layers) you have to change a few options..