| Probably one of the easiest (and free!) ways is XNView.
After installing XNView:
1 ) navigate to the directory where your image is located
2 ) open the image
3 ) select "image" "resize"
4 ) make sure the "keep ratio" box is checked, I suggest Lanczos resampling be selected in the lower pull-down box. You can either use a pre-set size from the top pull-down, or choose "custom" and type your own dimensions.
5 ) choose the size you want it to be
6 ) click on "file" then "save as" and select a NEW filename or it will overwrite your original.
XNView also happens to be my favorite image viewer. Did I mention it's also free?
It's also multi-platform.
You'll find most of the software I recommend falls into these categories.
I have two modes: wiseass and dumbass. Mode is determined by current blood alcohol level.
Drinking is a sport. In order to be competitive, you must practice on a regular basis. Although you can practice alone, it is much more fun to practice with friends. If you're out of shape and practice too hard, you will regret it the next day.
Life is a disease. It is sexually transmitted and always terminal.