Remove the staples from the lowest row of shingles, allowing them to be lifted up.
Staple tar paper to the part of the roof on which you're installing the metal paneling. Install the metal panels as recommended by the manufacturer, starting in the lower downwind corner of the roof. Work up the roof one panel at a time until you reach the shingles.
Lift the lowest row of shingles and slide the topmost metal panel slightly underneath the shingles, securing it to the roof as with the other panels. Continue installing the metal roof, starting with the column of panels just upwind of the first, until the entire tar papered area is covered. Install the metal roofing trim as instructed.
Slide an outside foam closure strip under the bottom row of shingles. This will fill the gaps between the ridged metal panels and the flat underside of the shingles. Run a bead of roofing sealant over the closure strip to secure it in place.