Compress the image using image editing software. One of the quickest ways to reduce the file size of an image is to compress it into a different format. Open your file in an image editing program (even Paint will work) and save it as a compressed file type. The most common form of image compression is JPG. JPG will result in a smaller file but with a noticeable drop in quality. Many image editing programs such as Photoshop will allow you to choose the quality of the JPG. The lower the quality, the smaller the file size.