I am not really sure if there is a question here other than to downsize the picture. I presume that means resize the picture smaller. there is a very small tool that is added to your right-click context called Image Resizer. it used to be a Windows powertoy but was rebuilt as open source. It can be downloaded at https://imageresizer.codeplex.com/

You right-click on one of the picture files on your desktop and select the "Resize Pictures" option. Then you can choose a preset size or a custom size. By default it will back-up the original picture in a folder called "Originals". Pretty simple to use.

You can also use a program like Photoscape (http://www.photoscape.org/ps/main/index.php). This is more of a photo editing product where you can resize plus do a lot more with the photo.