If you want to sharpen up the images on your storefront without spending money on high-end image editing software, there are a number of freeware graphic applications available online that provide much of the same functionality as their for-sale counterparts.
GIMP - GNU Image Manipulation Program - is a powerful application modeled after Photoshop. If you intend to do a lot of photo retouching, graphic editing, and advanced image manipulation and are willing to put in the time to learn, this is a great application with many plug-ins available to extend its capabilities.
If you need a basic application for image editing and manipulation, try Paint.NET.
For basic cropping, resizing, and format conversion, IrfanView is a great tool for batch conversion jobs.
We cannot provide support for these or other third-party applications, so if you have any questions, please visit the websites referenced above.