Remove the old weatherstripping by pulling it from the joint in the door jamb on pre-hung doors. Pry nailed-down weatherstrip from the face of the jamb with a flat pry-bar and scrape weatherstrip tape off with a razor scraper. Keep a piece of weatherstrip for comparison. Use the same or a similar style for ease of replacement. Replace the weatherstrip on both sides and the top of your door at the same time to ensure a good seal.
Measure and cut your weatherstrip to length to fit all three sides of your door. Scissors will work for most types, if your has a metal strip, use tin snips to cut it to length.
Shove the vinyl bead into the groove in a pre-hung jamb, reinstalling it in the reverse of removal. Use a putty knife or other flat, thin blade. Start at the top and work down. Nail metal edged strip to the face of the jamb with a small tack hammer. Use the nails in the strip for best results. Peel the protective layer from the back of adhesive weatherstrip about 6 inches at a time. Stick it down firmly, starting at the top and working in a straight line, keeping it against the door stop molding.
Remove the screws, using a cordless drill, and pry the threshold from the bottom of the door frame with a pry bar. Keep the old threshold for use as a template. Make sure your new threshold is the same height and width and at least as long as the original before marking or cutting.
Set the old threshold on top of the new and mark around it as a pattern. Cut the new threshold along the pattern lines with a jigsaw. File off any rough edges on aluminum thresholds before installing.
Run a bead of 100 percent silicone caulking around the outside edge of the threshold's bottom and set it into the bottom of the door frame. Tap it into place with a rubber mallet and drive one 3-inch treated deck screw through each hole in the top of the threshold to pull it firmly to the sill below.