Now that you have an image on your page. You may want to change it. To edit that image. Go to your edit page and click on the image and a box will come up above the image. See below.

Click on the pencil to bring up a box that will give the option of changing the placement and size of your image. The following box will open up giving you the choose of alignment, size and even replacing the picture you have. If you click on replace it will open up your media library where you can change the picture to any other one in your library.

Below is an example of the picture above. I have changed the size and the alignment. I have changed the image to medium size and the alignment so the image is on the right and the article on the left.