To change the order of your photos please follow these steps:
Login to BackOffice and go to Content > Pages > Primary Menu > Photos > Edit
Click on Edit Album for the album that you would like to rearrange the photos for.
Click on the photo you want to move on the white dotted bar on the left of the picture.
Drag and drop your selected photos from left to right depending on the order you want them to appear in the Album. For example, the first photo on the left will be the first photo online visitors will see in that Album.
Once you have rearranged the photos, click on the blue Save button on the lower right corner
Tip: you can apply the same technique to every slideshow in each article.