What they said is the easiest way to do it. here is a more complicated way.
right click on the file. choose open with, find photoshop, select image size, in the print dimensions choose something like 7.5 width or 10.5 height. save. file print, choose printer,select print. there ya go.
or open up in your browser, right click the image, choose print, find a setting in there that says, fit to page. then click print.