Replacing a broken asphalt shingle is a rather simple process. First you simply use a putty knife underneath and above the damaged shingle to break the seal holding it down. To remove the damaged shingle, wedge a flat bar underneath and pry upwards. As well, remove the nails holding down the shingle, but be careful not to damage the shingle above it. Cut off the damaged tab of the shingle with a utility knife, or remove the entire piece. Then you can simply slip the new shingle or tab in place, and secure it under the shingle above with 7/8” roofing nails. When the damaged shingle has been replaced, lift the tab up and apply a dab of roof cement to seal the asphalt shingles to the roof.