If you are the owner of an Album, you can change the order of images within it.
'Album order' is available as a customisable sorting option for search results. This can be useful, for example, if you wish for images to appear in a particular sequence in a PowerPoint presentation or Contact Sheet generated from an Album.
To reorder images, you must be viewing the files within the relevant album. Either search for the name of a particular album or select the Album from the Albums page, then select the 'View Files' button.
Select the grey area of an image thumbnail to drag images into your chosen order.