Scale down sprites of completed game?

I created a game with dimensions 720x1280 and published it to the Scirra Arcade, but the height ended up being too long

I'm having some issues resizing it down to 360x640.

I've tried to select all, and SHIFT + scale down, but sprites resize relative to itself instead of the whole selection. Also tried all the Configuration Settings > Fullscreen in browser modes after changing the Window Size to 360x640... no luck here either

The game has a dozen layouts. Is there an easier way than resizing each sprite individually

scirra.com/arcade/puzzle/17349/flat-bubble

USE SCALE.

I like to use a default scale multiplier which I apply to my objects.

global constant variable scale_multiplier = 0.04

each object has a instance variable called size

When created

Set scale: scale_multiplier*object.size