R, what is the pixel measurement of the photo you want to work with?
I would scale the photo first to either 2516 px length or 1158 px height and then crop it to the desired size. Would that work? Or if the original photo is larger, crop what you want to the required measurements.
EDIT: I'm assuming they've told you to change the resolution to 300 pixels per inch (the standard for print photos.) You need to do that first if you will be resizing the image, because 2516x1158 will be a different print size at 300 DPI than it would be at say, 72 DPI. Of course, if that's information you don't need, please ignore!