Hi Chunheng,

You have the ability to modify the screen size by hovering your mouse over the corners of the displayed box, click and drag to make the screen larger.

If you are looking to get your image file bigger than what can be displayed you may want to add this as an attachment so that when you choose to view it will download the image file to open using your windows default image viewer.

If you need to have better scrolling and sizing in the input portion you should enter an Idea for them to provide better scaling. 

Thanks