Paint can resize images (with horrible quality), but it will not offer any reasonable control over the filesize.
The websites
here can do mediocre filesize optimization for free, but won't actually change image dimensions.
What you need is an image editing program, such as Adobe Photoshop, Photoshop Elements (cheaper version), Corel Painter, Jasc Paint Shop Pro, etc etc...there are a number available.
One such program that's free is
The Gimp, but it might be a little harder for a novice to use. Hmm, I can't think of other free programs that will resize & optimize images with decent quality.