To Send One or More Images to the Back in the List

In the Raster Manager dialog, select the name(s) of the required image(s), or use the Raster Selection tool to select the image(s) in the view(s) .
From the Display menu, choose Send To Back.
The selected image name(s) moves to the top of the list. Simultaneously, the view(s) in which the image(s) appears updates to show the selected image(s) behind any other overlapping images.