xbmbrowser will show you all the bitmaps in the directory if it is specified otherwise it will look in the current directory. Note that if the program can not change directory to the directory in the command line it will exit and print an error message.
You can then select any bitmap that is displayed and you will be able to Rename, Copy, Delete, Edit and Set it as the root window bitmap. (Edit and SetRoot may not work on your installation - you will have to try it to find out).
xbmbrowser will take all the normal Athena Widget toolkit options it is given.
For instructions on how to use it, start it and press the Help Button.