I’ve had good luck with Postimage , there’s an option to resize images for forums.
And the basic plan is free …
https://postimages.org/
It’s straightforward to set up and navigate.
Here's what I don't like about PostImage.com...you lose all control of any image you upload.
"With regard to any file or content you upload to the public portions of our site, you grant PostImage a non-exclusive, royalty-free, perpetual, irrevocable worldwide license (with sublicense and assignment rights) to use, to display online and in any present or future media, to create derivative works of, to allow downloads of, and/or distribute any such file or content, including embedded (hotlinked) into third-party websites otherwise not affiliated with PostImage. To the extent that you delete any such file or content from the public portions of our site, the license you grant to PostImage pursuant to the preceding sentence will automatically terminate, but will not be revoked with respect to any file or content PostImage has already copied and sublicensed or designated for sublicense."
If it's too large, just launch Paint (in Windows), drag and drop your image and click on Resize.
I tried that using the "Resize and skew" function in Paint, but although the number of pixels are reduced the file size stayed the same. The free program from Irfanview.com (been using it for 15+ years) seems to work better.