Change resolution and format of Sprite Packer Atlas

I have an atlas created by the sprite packer and I want to reduce its size (to 1024x1024 or 512x512) and also change the format (to DXT1 or DXT5).

Is there a way to do this straight from the atlas or do I need to change the resolution and the format of all the assets that have the atlas' packing tag ?

Thanks.

![alt text][1] [1]: /storage/temp/35204-screen+shot+2014-11-13+at+7.31.02+pm.png