If you want to reduce the size of your image, click into the Wdith field and set the percentage size of the original, for example if you want to half the size of the image type 50%. After you hit the Enter key on your keyboard the size will adjust
Click on the insert image button (as shown below)
Click on the Drop Image (or click) box. You will be able to now select an image from your device and this will then be inserted in to the text area of the editor.