Microsoft Paint is a simple image editor/converter that is available on any Windows machine. To open an image in Paint, simply go to your pictures folder and:
You will notice that this image is actually huge (only a fraction of it is actually shown here) - way to big for publishing in a typical webpage or blog. From the top menu in Paint, click on "Image" and then on "Resize/Skew" to re-size the image down to a smaller size.
Change both the "Resize" options of "Horizontal" and "Vertical" from 100% down to 25%. Then press "OK".
The image will size down to a smaller size (if you want to undo this, click "Edit" and then "Undo"). Once you have the image to the size you want, you need to save it as the right file type.
That's It! Your image is now ready for the Web.