The magnifying glass runs from a bit of Java script found in the 'Head box' on the Element pane. In the 'Footer box' there is some further script, the actual initialization. If you open that script, right at the bottom of it you will see this line:
The number is showing how strong the magnification will be, in this case 3 times. It can be edited. The limits will of course depend on the size and quality of your image.
The size of the actual magnifying glass can also be edited. Here it is set to 100 x 100px for viewports below 600px wide and to 150 x 150px for larger viewports.