A popular style in web design today, is background images or coloured bands, that stretch across the entire browser window, with the rest of the content is centered. This effect is called “full bleed”.
To enable this for certain images or other objects on your page, select those objects, and find the Effects tab on the your design palette. There you will find a checkbox to enable full bleed this behaviour for the selected objects. the full bleed effect won’t appear in the editor, so you have to Save your page and press View Live on the toolbar.
When objects are full bleed, you'll be able to re-position them vertically, but not horizontally because they automatically span the entire width of the page.