I don't think the software will run on Mac OSX Sierra because if Mac OS apps are not properly updated to support a certain version, the the main OS won't actually allow you to run it.
Use the App Store and then look for other Photo Editors because there are plenty available. For professional editing, try Adobe Photoshop or Adobe Illustrator (vector design).
You can download them from the following page: http://www.adobe.com/downloads.html
