Pre-hung doors are quite easy to install, but removing them can pose quite a challenge. Because pre-hung doors may have been fit in place with nails, shims, or screws, you will typically find that utilizing a saw with a metal-cutting blade will speed the process along. Be sure to follow safety guidelines and wear goggles and gloves if you so choose.
You will have to remove the trim from the door with a pry bar. If you are planning to reuse the trim, make sure to remove it gently, one piece at a time. There will most likely be nail holes that you want to have filled, but once you have the new door hung and are ready to reattach the trim, you can fill the holes with wood putty and paint over them.
If you are planning to replace the trim, you should still remove it gently. The old trim will serve as an excellent template for the new trim. Because the measurements will be the same and precise, you will be able to cut your new pieces correctly, and precisely.
Separate the Door from the Frame
In order to separate the door from the frame, you will have to remove the hinges and check for the long screws that run all the way through the doorframe. You will have to remove these screws using a screwdriver or a screw gun. You must take great care in lifting pre-hung doors from their frames because, depending on the style of the door, it can be very heavy. Find someone to help you while you slowly remove the door from the frame.
Loosen the Doorjamb
With the door out of the way, you gain direct access to the doorjamb. This will probably be the most difficult portion of the job because of nails and shims. Most of the nail will have been pushed down and covered with putty. Your best bet is to free the jamb by cutting it out with a reciprocating saw fitted with a metal-cutting blade. The saw is able to cut through the nails with ease. If you know that the door was set with screws, the saw will work but it will take considerably longer to cut it loose.
Remove the Doorjamb
Push the doorjamb out of the opening. Be careful not to stick yourself with nails or sharp edges. If you plan to replace the threshold, now would be the best possible time for you to do it.
Before you leave the job site or install new pre-hung doors, you will want to make sure the opening is free of nails or sharp objects. If you see any, try to remove them or countersink them with a nail set. If you see any old insulation or hardened caulk, you will want to remove that as well.