The area that is “covered” by the image is called the image’s canvas. This effect will allow you to change the canvas’s size. You can select at which position the current canvas should be placed.
Select the "Change Canvas Size" option from the Recipe Panel's <Editing> drop down and then "Size & Crop"
By default the width and the height fields are filled with the current image setting. Specify a new value, for example a larger value. If a larger value is specified, there will be some white space. Select the color you want to use to fill up this white space by using the “Background Color” field.
Finally select where you want the original image to be positioned on the new/resized canvas.