Oh! I actually found a quick release lever on the caliper. When I think of caliper, I think of the metal piece that holds the brake pads in a U-like shape over the wheel. I just saw one screw attaching the caliper to the frame.
But now I checked on the cable running above the caliper to the front of the bike, and I found a little lever. And it was in fact loose!
Thanks a lot for your help, guys!