Clear any debris from where you plan to place your ladder for a stable placement. Stand the ladder against the house beneath the shingles you want to replace.
Rip the shingles from the roof by hand. Use the claw end of the hammer to rip away any stubborn shingles.
Lift the bottom half of a remaining shingle. Slide the tab end of the new shingle beneath the old one, and nail the new shingle into place with three roofing nails. The shingle at the gutter should extend approximately two inches beyond the roof and into the gutter. Repeat across the roof until you have replaced all the shingles you removed.