How can I make a 3 megabyte photo file smaller?

Changing the format to JPEG should cure the problem. Most likely your original photo will already be in .jpg format. In the photo management software, free ones or even the ones built in the operating system of the computer you can do few things to reduce file size of the photo. You can either resize the image or use more compression. Resize will reduce size of the image (number of pixels will reduce) and compression will reduce overall quality of the image. When you use save as .jpg most software will allow you to select the compression level you want to save the image with. - Neeraj Sharma