Method 1: Use the corners
When you select an image, there are hot points on all corners and edges of an image. An image can be resized by clicking and dragging those hot points. Make sure that you are only using the corners since using the edges will distort the image.
Question: What if I accidentally distort an image? How do I bring it back to its normal proportions?
Answer: In the Image Properties, click the blue padlock so that it’s locked. This will restore its original proportions. (See Method 2 for details)
Please note: Hot points are not available in Chrome, so if Method 1 is for you, use Firefox instead.
Method 2: Adjust the Image properties
a) Select the image, b) Select the Image tool in the WYSIWYG toolbar, c) Make sure that the blue padlock is locked (next to the height and width properties). If the padlock is unlocked, click on it to lock it.
d) Adjust either the height or width. If you adjust the height, the width will automatically change in order to retain proportions and vice versa.