The reasons are numerous to replace an exterior door jamb. The jamb may be damaged due to years of use, or you may want to update your home with a new look. The door unit is made of four sides. The bottom of the door is known as the sill or threshold, and can be made of wood or aluminum. The hinge side of the door unit is referred to as the hinge side jamb, the top of the door is the top jamb, and the locking side of the door unit is known as the lock side jamb.

Instructions.Things You'll Need:
•Flat prying tool
•Hammer
•Reciprocating saw
•Screw gun
•Flashing paper
•Replacement exterior rated door jamb
•Wood shims
•4 foot level
•Straightedge
•Brad nails or finish nails
Step
1Remove all of the door trim from the exterior and the interior sides of the door using a flat head prying tool.Using a reciprocating saw, cut all fasteners that hold door jamb in place; this is done by sliding the blade of the saw between the door jamb and the rough frame opening.

Step
2Using a screw gun, remove any screw fasteners that may be holding the threshold in place. Slide the old door jamb out of the rough opening.

Step
3Prep the rough opening for the new door jamb by removing any leftover nails from the rough framing. Replace any paper flashing around the rough door opening that may have been damaged.

Step
4Slide the new door jamb into the rough frame opening. Use wood shims under the sill of the door to level and adjust to match finished interior flooring.

Step
5Place shims at the bottom of the jamb between the rough framing and side jambs to center door frame in rough opening. Secure the sill of the door jamb with screw fasteners.

Step
6Secure the jamb at the lower hinge side with brad nails. Use a straight edge and level to plumb the hinge side of jamb, and then secure the top of jamb into position using brad nails.

Step
7Place the straight edge against the jamb and secure the hinge side with brad nails. Position the shims as required to straighten the jamb. Nail directly through side jambs and shims into rough door framing. Repeat this on the lock side of the jamb and the top jamb.

Step
8Replace the interior and exterior trim around door using finish or brad nails.