Use a program such as Microsoft Paint (comes with Windows) or IrfanView
Open each image and resize to about 40%. This will decrease the size without making the image blurry.
For Microsoft Paint: Select "Resize". Enter 40 for the horizontal or vertical value. Click OK.
For IrfanView: Select "Image". Select "Resize Resample". Select "Set new size as percentage of original." Enter 40. Click Ok
