Here are two ways to resize a couple of images.
1. Using this website called picresize.com, link here. You can upload more than an image, choose a new size, smaller with 75%, 50% or 25%.
You will be able to download a zip archive with the new resized images.
2. Using “Image resizer for Windows”. Link here. This is a free and very small program that works great with Windows 7. It will create a new option for when you right click on an image or a couple of images.
It has a few options to resize your images, however, it has pixels instead of percents.
Overall it works ok but it would really need an option to resize the images to specific width/height and still keep the aspect ratio (it should detect the aspect ratio for each individual image).