Better install the Gimp then (
http://www.gimp.org/), it is the freeware open source equivalent of Photoshop.
To use it for resizing an image: open the image in Gimp (on Windows, use the executable gimp-win-remote.exe), then go to menu "Image" and "Scale Image...", and go from there. Slightly outdated tutorial can be found here :
http://docs.gimp.org/en/gimp-tutori...ckie-scale.html .