Click the 'edit' icon (pencil). I'm not sure you can actually remove the preview, but you can change it to be the same as the main view which will do.
Also note that you should still be able to use a rejected piece as av, saying this for your previous rejected pieces.
Thank you Manupix for getting back with me. How do you get rid of the preview? After you have submitted it to the gallery?
If you want the main image to be your av, you've got to get rid of the preview.
Dude you Rock Thanks so Much! YOU ROCK MANUPIX!!!
Your friend,
Morintari