Reducing file size (with the least change to print quality)

[Moso]

I apologize in advance if this has been covered elsewhere. I've read through the forums, but this is new to me and I'm not sure if I'm understanding everything correctly. I'm trying upload about 250 photographs (JPGs) to a photo sharing and printing service for a friend. Since I can't do this without being charged additional fees by my ISP, I want to reduce the size of the files. The image size is now 3888 x 2592 pixels, and the print size is 137.2 x 91.4 cm (54.0 x 36.0 inches). When I look in Image Properties, the resolution fields are blank. The printed photos need to be high quality. Should I use batch conversion to resize the print size to 15 x 10 inches with a quality setting of 75? (The photo service's recommendation for their prints is Photoshop Save As at JPEG 10. Their printers run at 302 dpi.) Should I change any other settings in the batch conversion? Any help would be greatly appreciated--Thanks!

[MItaly]

You can save them in JPEG at quality 90 (at most 80, then you'll start to lose seriously quality). Absolutely do not resize them, since they are already quite small for the paper format you're going to use; in facts the print resolution will be of 72 DPI (3888 px / 54 in = 72 DPI; 2592 px / 36 in = 72 DPI).

[Moso]

Thank you for your response. I appreciate it a lot. If the photos were printed at 15 x 10 inches or a smaller size, is there anything I could do to decrease the size of the file or increase the quality of the image?

[Frank]

First change the save quality of your pictures (using 'Batch Conversion') and then try JPEGCrops!

Using this tool you can select any wanted picture format!
See the thread: "Try the best tool for this task - JPEGCrops..."