Changing pixels on a picture to a LOWER number

I took some pictures at a higher pixel number than I was supposed to and I need to change the pixels to 640 X 480. I know I can do this in paint, but when I do it crops my picture (almost in half). Months ago I downloaded a free trial from PhotoImpression (Arc Software) and was able to fix the photos with ease, but my computer crash and I no longer have the program and am not eligible for the free trial anymore.

Can anyone suggest a fix? I need these pictures fixed tonight and I don't want to buy a program. I'm pretty computer 'stupid' and want just a basic fix.

Thanks!