Measure the width of the staircase, using a measuring tape. The edging does not have to go all the way across, so this measurement can be adjusted.
Mark on the edging the desired length using a pencil, marker pen or piece of painter's tape.
Insert the edging into a vise so the right angle of the trim comes over the top of the vise jaws. Ensure the edging is tightly secured before sawing begins.
Cut the edging to the required length, using a hacksaw with a blade suitable for cutting metal.
Clean up the ends of the edging using a piece of steel wool until all sharp edges are removed.