To change the order of thumbnails in a study, select the icon on the thumbnail. A blue box will appear around the thumbnail (shown below) - drag the thumbnail to its new location within the study.
Repeat the process for any additional thumbnails you would like to move.
This feature is useful if you would like to compare two specific thumbnails (from the same study) in the viewer by choosing a split-screen format. The viewer will always display thumbnails in consecutive order; if you want to look at three images side-by-side, arrange them next to each other on your study list.
If you want to compare thumbnails from different studies, select the desired thumbnails in each study and choose Compare from the study menu.