How to adjust the image widget size: 

To resize an image in a canvas widget, first hover over the widget and click the pencil icon. Next, click on the image. Finally, drag the red line of the item to top, bottom, left, or right to adjust the size. 


You can edit any one of the elements of the canvas widget (i.e. image, header, and color). In this way, you can adjust the height and width to the desired size.

Here is how to adjust the image widget size:

Step 1: Hover over the Canvas widget and click the pencil icon. (How do I enter an items editmode?)
Step 2: Click on the image widget and grab the red line.
Step 3: Drag either top to bottom or left to right until it reaches your desired size.
Congratulations you have resized your image!
Note: You can adjust the other elements in the same way.