If you don't have photoshop, try paint (comes on 
all windows OS).  Open up the file, choose Image, 
stretch/skew, and under stretch, make sure that 
you change both vertical and horizontal percents 
by the same increment.  Then when you have it the 
size you want, save the file again.  Photoshop is 
much better, but if you are making the images 
smaller paint is not too bad.