Thanks to retzev we've been made aware of an excellent Web site with tools to help those with "almost no graphics skills or knowledge" resize their image files:
Shrink Pictures. The site will process images up to 6MB so long as they're in jpg, gif or png format, and the resulting resized images are automatically converted to jpg, which is the preferred format here on the forum. Extra tools (through the free Google Pack) can even be added to crop and sharpen images.