Brakes problem
1997 BMW 328 6 cyl Two Wheel Drive Automatic 145000 miles

I am replacing the front brake pads on my son's BMW 328i 4 SDN. Here is my problem... I loosened up the front calipers to take the two bolts out that hold the whole program together. I used an Allen wrench to take the top one out and when I went after the lower one ...it didn't like the size of my allen wrench as much as the top one and it went about one full turn and sort of stripped it out a little anyway now what? is there a special tool that I was supposed to use ?? how do I get this 2nd cliper bolt out ?? it's possible that the right exact sized allen wrench tool end that fits would have no problem ...any advice?? help