See the help menu

At the right end of that bar across the top is a help menu, and if you follow a reasonably obvious path in you’ll end up here:

https://model-railroad-hobbyist.com/help/how-to-post-an-image

And that explains resizing, among other things.

Thanks

Thanks, Ken, from that I was able to resize to get the whole photo in the MRH page.

If you want to resize photos

If you want to resize photos in general (not just for MRH), I'd recommend https://www.irfanview.com/.It's free and quite versatile.

I second Irfanview

Nearly all the photos from my recent NMRA/NTS shoot were resized with Irfanview - even the ones that were originally processed with Photoshop. It makes a photo that both looks good and takes up a miserly amount of KB in storage.