To edit graphics which have been uploaded, click the image icon in the Page Editor as if you were going to insert an image. On the right side of the "Source:" box, click the folder icon to enter the Asset Manager. As you can see by the illustration, the picture in the library is quite large. To edit that picture, click on the small pencil icon next to the name of the picture. This will open the NE1 Image Editor, which allows you to edit a picture directly online. From there you can edit the size of the graphic, rotate the picture, crop (cut out parts) the picture, or even adjust the color and brightness of the graphic.
*Tip: When editing a picture in the Image Editor, you can always return to the way the picture was originally by clicking the "View Original" button at the top of the Image Editor window.