Open the door. Remove the all of the existing weatherstripping from the doorway. Remove any tacks or screws used to secure the old weatherstripping. Also scrape any remnants or adhesive with a putty knife or scraper.
Read the correct positioning of the weatherstripping type you have, then measure the height of the door opening where the stripping will be applied, from the top surface of the door's threshold to the end point on the door jamb.
Cut two lengths of weatherstripping to the door height measurement with a utility knife for vinyl types of weatherstripping or a hacksaw for metal reinforced stripping.
Position one of the lengths of weatherstripping against the inside surface of the trim edge of the door jamb to check that the weatherstripping will press firmly against the door surface when closed. Then attach with the adhesive or fasteners provided.
Repeat Step 4 to attach the weatherstripping to opposite side of the door opening, again checking that the weatherstripping presses firmly against the door surface when it's fully closed.
Measure the width at the top of the door opening, then cut a length of weatherstripping to this dimension.
Install the top piece of weatherstripping to the door jamb header using the adhesive or fasteners provided, after checking that the weatherstripping will press firmly against the door when it's closed.