Hi Tim

there are 2 ways
the normal way is to unclip the back with that little clip on the top left of the rear standard
take off the ground glass/film holder and rotate it to portrait and clip it back on
another way is to slacken the rail holder and tilt the whole camera off to the side into portrait mode but this makes operating a bit awkward and puts the tripod off balance a bit which mat cause other problems

hope this helps