Change Sizes Quickly

So to upload to Scirra Arcade I need max 800 width and mines at 1280 (screen width size I'm assuming). Is there anyway I can change the size of everything in my project quickly without having to do it one by one?

That makes sense for the window size. But how do I scale the objects with it as well? They stay the same size when I change the window size.

I havent tried to upload to the arcade so im not sure what the problem is, i thought that might be it =x

I just ended up uploading it to googledrive instead of scirra but thanks anyways!