Ah. Sorry to say there is no way to rearrange photos in the Photos app.
The ones in the Saved Pictures Album are arranged by date saved to the album. The synced folders are arranged by date and time the photo was taken. You could probably edit the date on the pictures on the computer, but that's a poor solutions.
There are other photo display apps out there. I can't really recommend any, since I don't use them. But they will give you more options, everything from quick slideshows to professional portfolios.
Another options is to upload your photos to your favorite online service and use one of several excellent apps for managing and displaying them. Picasa, Filckr, and Photobucket all have very good apps. The down side is you need an internet connection to show off your photos.