Using irFanView to batch edit images

I recently decided to repurpose a product and turn it into a book and Kindle version. The Kindle version had no real issues with images since they get down sampled anyway, but the printed book needed to have the images at at least 300 dpi (dots per inch). If not the images would almost certainly be grainy, and I don’t want that. Most screen capture software saves the images at 96 dpi or sometimes 72 dpi.