Remove any existing bullnose from the stair treads overhanging the riser by cutting the treads flush with the riser surface with a circular saw. Cut the edges of the treads sitting against the skirt board running the length of the stairway, where the saw base won’t allow you to reach, with a flush-cut saw.
Measure the risers for each step with a tape measure, both riser height and width. Cut the laminate floorboards to match the measurements with a table saw, cutting both to fit the length of the risers as well as the height. For the height, make two cuts along the floorboards, removing both the grooved edge and the tongued edge to create a riser in the size needed.
Place a zig-zagging bead of construction adhesive on the rear of the riser board. Press the board onto the front of the step over the existing wood riser, and then secure it into place with finish nails driven through the base and along the top of the riser every 6 inches with a nail gun.
Place two wood screws through each existing stair tread into the stringers running along the side of the stair beneath the step to prevent squeaking. Use a drill with a screw bit attachment to speed up the screw work.
Measure the length of each existing step tread, and then cut the laminate boards with a table saw to match the measurement. Cut a length of bullnose molding to match the length of each step.
Measure the width of the stair from the riser surface along the back to the front of the step, and then measure the bullnose molding strip that you’re installing to the front of each step to create the rounded overhang extending 1/2-inch over the front of the step. Subtract all but 1/2-inch of the molding width from the stair width measurement, and then make a cut along the grooved edge of the plank, leaving a smooth edge that will serve as the rear of the tread, and making the plank wide enough to fit on the stair with the molding attached while maintaining the overhang desired.
Test the fit of each step, attaching the laminate bullnose strip along the tongue of the board, and then setting the plank onto the stair. Make any adjustments necessary to the cut before placement.
Place a zig-zagging bead of the construction adhesive onto the existing wood tread. Press the laminate stair treads onto the step over the adhesive. Secure the tread into place with finish nails driven through the board at the corners and into the old wood tread.
Place a bead of the adhesive along the tongue of the step and another on the base of the molding. Slip the groove at the rear of the molding onto the tongue of the step and then press the molding onto the step edge. Put a nail into through the face of the molding at each side and into the step to secure it firmly into place.
Drive the nails beneath the laminate surface with a nail set, and then cover all of the nail holes with wood putty tinted the same color as your laminate boards.
Place masking tape along all of the joint edges. Caulk the seams along the edges of your risers and treads. Allow the caulk to dry, and then pull the masking tape off, leaving sharp caulk lines. Paint the caulk with a small paintbrush to match the laminate.