There are two methods in which you can resize a block on your canvas.
1. Drag the bottom.
Click on the block you want to resize to select it. Move your cursor to to the bottom of the block. There will be a white bar defining the boundaries between the blocks. A two way arrow will appear when you mouseover this bar. Click on it and drag to resize the block. A black box will appear to show you the size height to guide you as you resize.
2. Using the block buttons.
Click on the block you want to resize to select it. Six buttons will appear to the left of the block. The button at the bottom is a gear for Settings. Clicking on it will allow you change the canvas width and block height.
Kindly note that you cannot change just an individual block's width. The rest of the canvas will change along with it - not just the selected block. Block height can be set individually.
From the top, the block buttons allow you to: