Since you probably don't want to change the size of each original image, only its size on the composite page, drag an original image onto the large page, then Edit > Transform > Scale. Hold down the Shift key to maintain proportion and drag a corner handle to reduce the size of the image on the page. Repeat the process for each image. If an original image is far larger than your composite page and the Transform handles are not visible after bringing into the large page, hit Cmd+0 (that's Cmd+Zero) so that the Transform frame and handles are available. Good luck.