You can resize two ways.
1. Use the crop tool in
PS. Set the size to 5 x 7 at 300 ppi. Drag the tool across the image and get as much of it as you can without going outside its boundaries. You can move the rectangle around to optimize which part of the image you are prepared to sacrifice, and then hit OK or enter.
2. Use the rectangular marquee and set the pull down menu in the options bar to Fixed Ratio and enter 5 x 7. Drag the marque and move it around, then do Image>Crop. If the resolution is different from your final requirements, you will need to do Image>Image Size to resize it.
Unfortunately you can not use the transform tools to resize just the length or width without distorting the image.
Regards, Murray