There are return springs to pull the pads away from the rim. Either you can simply bend the left one out a little, or there should be small adjustment screw(s) down by the base of the brake arm. turn the left one in and the brake should spring out more. Or you can pull the brake arm off and reset the anchor point of the return spring one notch higher. I'm sure there's a nice walk-through of how to do it on
www.parktool.com