there are probably online editors you don't even need to download software if you don't mind leaving a copy on their server. Like what are they gonna do with it?

How do I download it to my desktop, which is how I normally post images, then use the editor but I don't resize things, I haven't tried that before. Then how would I get the avatar uploader to use a link from the image hosting site? That's the part I am lost about.

That's $49.95.

There was no charge on the weekends!

You right click and save to your download folder. There might even be a choice to download to desktop.

From the download folder you copy and paste, or drag, to desktop.

At that point the file is yours, you don't need to worry about the online software editor anymore.

I'll try that. I'm reluctant to try by error online.

What worked was choosing the avatar resizing option from the many listed, when the image shows in the little window to the left (on PostImages) it opens the file from which you can download with "save image as..." from there it all worked!

I take a gazillion photos, and am constantly resizing.
I use two apps on the mac: SuperPhotoUpscaler or BatchPhotoResizer (cuz they'll do several at a time)
Preview app (or any viewer on any computer) should offer you a "save as" usually with resizing options,
but the easiest for mac folks is to email themselves (or others) a photo, and the Mail app will ask you if you want to resize it, full, large, medium or small. It ain't elegant, but it's easy.

If you can't right-click (control click on mac) to save an image, you can almost always just take a screenshot.
Built-in screenshot capability or apps have a way to save just an area you select, not just the entire screen.

Of course, I sometimes "edit" photos to make a fun meme, but that's another story altogether.