What image viewer do you use? There should be a feature to resize in it.
If not, get infranview here:
http://downloads-zdnet.com.com/3000-2192-10021962.html
It is a great free picture viewer.
Open your image in it, then got to: File, Image, Resize and choose "Set new size as percent of original"
60% of the original size should probably work on this file (and make sure you check the "preserve aspect ratio")
Hope that helps