// @Double(value=1.5) xScale
// @Double(value=1.5) yScale


// Scale image
//run("Scale...", "x=&xScale y=&yScale interpolation=Bilinear average create");

xScale = 0.5
yScale = 0.5

// Iterate all ROIs in ROI Manager
for (i=0; i<roiManager("count"); ++i) {
	roiManager("Select", i);
	
	// Scale ROI
	run("Scale... ", "x=&xScale y=&yScale");

	// Replace old ROI with scaled one
	roiManager("update")
}