You can put your cursor on a handle and push or pull vertically, horizontally and diagonally.
When you pull a handle horizontally the picture gets distorted (and the world is suddenly oval)…
Or, when you pull a handle vertically, the picture gets distorted (and the world is suddenly egg-shaped)…
But, when you drag a corner handle and put your finger on the Shift key on your keyboard at the same time, the image resizes proportionately. Make it bigger (see the pitfalls of that in the previous post)…
Or make it smaller. It’s not rocket science.