To install a pre-hung exterior door, start by removing the old door and trim from the opening. Next, measure the opening and cut the new door to size. Then, attach the hinges to the door and hang it in the opening. Finally, attach the trim around the door.

Here are the steps to install a pre-hung exterior door: 1. Remove the old door and casing, if there is any. 2. Check the framing around the opening to make sure it's even and plumb. If it's not, then correct it before installing the new door. 3. With the help of a friend, lift the new door into place and secure it with screws or nails, making sure it's level and plumb. 4. Install the hinges on either side of the door and attach them to the framing members. 5. Hang the doorKnob or handle hardware using screws or nails from inside the house (or use a screwdriver or drill).