OK, Lou! Whatcha do to get that reasonable size pic below the thumbnail? Like I told Stig, explain like you would a four-year-old!
I probably should have just asked my six-year-old to do it. I'll do my best, though...
Go to your photos, right-click the one you want to re-size.
Scroll down to "Edit With"
Select "Preview"
When the pic opens up, go up to to "Edit"
Scroll down, choose "Select All"
Should appear outlined, like this:
Go to "Tools"
Select "adjust Size"
I just adjusted the width... make sure you have "Scale Proportionately" checked.
Click "OK"
I like to re-name the file, to note the modification.
Upload to your favorite pic host... ImgBB in my case.
Hope I'm not leaving something out.
Edit: And I still didn't re-size this one properly!