No problem. I first rename the comic-reader file's extension to an archive format (from either cbr to rar or cbz to zip), then expand the archive file's contents into a folder. I open each of the files in Photoshop, and do a 'Save for the Web' (cntrl+alt+shft+S), which opens up a new window showing the file as a recompressed jpeg, with a settings box that lets you pick the compression ratio, from "0" (totally compressed) to "100" (no compression). It will tell you the ultimate file size of the recompressed image and previews how the image will look, so I fool around with the compression ratio that yields an image size of ~500-800Kb, making sure the image doesn't look overly compressed (grainy or blocky).
I run through the entire folder of original images, and save the compressed images in a new folder. When I am done, I go to the new image folder, highlight all files, right click and select 'create archive'. This creates either a rar or zip file (you choose which, doesn't matter), which you then rename to either a cbz or cbr.
Voila! A smaller, kinder comic. Be careful, tho. Compression degrades the images quality. Overly compressed images are hard to read, and once the quality is lost, it cannot be restored. Try to strike a balance between file size and quality.
