Are you talking about the body mount bolts on a sidekick or tracker?
If so, "under the cowl".. are you talking about right behind the bumper and grill?
You will need to remove the bumper, and inner bumper, if you have not already done so. Then, you will also need to remove your grill, and the headlights. Now, there is a bolt head on top, and you should be able to look under now, and see where it comes through the bottom. Just put a socket (you might need a deep one) on top and turn it. The bottom is threaded through a nut that has been welded to the frame.
If it's hard to get loose, let some WD40 sit on it for a little bit, or take a torch to it and heat it up some.
That should work.. My front two mounts were a peice of cake. It was getting the two under the cabin on each side that was hard.
Heather