1 Reduce the size of the photos so changing their positions is easier. They are far too big.
2 Delete all photos at once, or download them all to rearrange them on my PC and re-upload in order of appearance?
Working with large photos is difficult, so either making them thumbnails and/.or downloading and renumbering 1 though 50 before resending will make the process easier?
On my Windows laptop when I am doing this, I press Control and the minus key a few times and that reduces the size of the page you're viewing. Once you're finished, press Control + the same number of times and you're back to the right size. On a Mac I think it would be the Apple key instead of Control.