Door frames or jambs can be removed for replacement, to change door swing direction, or to gain a bit more space to move furniture. Door frames are nailed to studs. Most of the frame is covered by trim. After the trim is removed, the frame comes out easily.
Removing an Interior Door
Open the door. Remove the screws holding the hinges to the jamb with a drill/driver. Lift the door out of the opening. The hinges should stay on the door.
Cut the caulk or paint along all edges of the door trim, or casing, using a utility knife. This prevents the caulk or paint from peeling off of the wall when you remove the casing.
Insert the tip of a pry bar behind the casing. Pry it upward to loosen the nails and remove the casing from both sides of the door.
Knock as many shims out as possible, using a hammer and a wood block. Shims are small pieces of wood -- typically cedar -- wedged between the jamb and rough opening to plumb and level the door. Some may have nails through them and won't budge. Others will pop right out.
Remove the brass strike plate from the jamb by removing the screws with a drill/driver. It's not always necessary to remove this, but there's occasionally longer screws that penetrate into the rough opening. You're more likely to encounter them on exterior doors.
Insert the metal-cutting blade of a reciprocating saw between the door jamb and rough opening. Slide the blade around the perimeter of the jamb to cut through the nails.
Slide the frame out of the opening. If it resists, check for nails or screws you might have missed. Tap the frame out with a hammer and wood block if it's stubborn.
Pull out the cut-off nails with diagonal pliers. If they resist, hammer them down. Scrape off any remaining caulk or paint. Tuck loose insulation back where it belongs.
Removing an Exterior Door
The removal of an exterior door is much the same an interior door, except that the exterior molding is typically made with brick mold, which is thicker than interior casing, and the threshold typically comes out with the frame.
Open the door and remove the hinges holding the door to the jamb. Remove the door from the frame.
Insert the tip of a pry bar under the interior casing. Pry it off and remove it.
Insert the tip of a pry bar between the door jamb and the brick mold. Pry it away from the jamb. It will require more effort than interior casing. Work your way around the door, prying where needed until the brick mold lifts away from the frame. It may come off in one piece or break into three pieces.
Use a hammer and wood block to knock out as many shims as possible, just as with an interior door.
Remove the screws holding the brass strike plate to the door frame, as well as any other deadbolt or security lock plates on the frame. Exterior doors often have long screws that penetrate through the jamb and into the rough opening.
Insert a reciprocating saw blade between the frame and rough opening. Cut off all the nails around the perimeter of the frame.
Remove any vertical screws from the threshold. Insert a pry bar underneath it from the exterior side. Pry up gently to loosen it. The threshold may separate from the frame when you remove the frame from the opening. That's OK.
Tap the frame from the exterior side, at the top with a wood block and hammer to tilt it inward. Remove the frame from the opening by pushing/pulling it into the interior.