Hi Janice,
Are you talking about sharing the treasury on Facebook?
If so, there are little arrows that show up in the box as you post that let you scroll through the thumbnails and pic which pic you want as the main one. You can also go back in and rearrange after,but only for a limited time I think.
You could also go into your treasury and use Edit to rearrange your pics of course.
If you want to show the whole treasury, you can take a screen shot or grab or capture (different depending on what browser you are using) of the whole page and post it.
Hope this helps! Good luck. : )