1.Prepare a new door.
Measure your current door for width and buy a door of this size. You should also look for a door as close as possible to the height you need, but some trimming may be necessary.
Double check the door measurements against each other before installing the door.
2. Remove the hinge pins. Using a hammer and nail set, remove the hinge pin that connects the two sides of the hinges. Be careful, as this will release the door.
3. Remove the door. Set the old door aside and remove the hinges and hardware.
4. Set up the doors. Set the new and old doors on a set of saw horses, with the old door on top. Align their hinge side and top and then clamp them together.
5. Mark the cut points. You'll need to cut a mortise (indent) for the hinge, as well as the hole for the door handle. Trace the door handle hole or holes from the old door onto the new one. Then, measure and mark or trace the hinge shape on the new door, using the new hinge or the old one (if the hinges are the same size) as a guide.
6. Trim the rest of the door. Measure, mark, and then trim the rest of the new door with a circular saw, so that it is the correct height and width.
7. Cut the mortise. Using a hammer and chisel, cut the mortise for the hinges.
8. Mark and drill pilot holes. Using the new hinge a a guide, mark the location of the (usually) three screw points and drill pilot holes.
9. Cut the lock set holes. Using a kit will be easier than measuring and cutting for yourself and they are cheap and readily available. Just place the jig at the hole you marked from the original door.
10. Sand and paint the door. Now is a good time to sand and paint the door, if you want to.
11. Attach the hinges and lock set. Install the hinges and lock set. Follow the manufacturer's instructions to install your particular lock set correctly.
12. Remove and replace the old jam hinges. Remove the old hinges and then replace with the other half of the new hinge. Use a chisel to deepen the mortise if the hinge is not flush with the edge of the casing. You can also replace the strike plate if a new one was needed or included with your door handle.
13. Set the door. Set the door on some shims and slide it into place. Set the pins and test the door. If it works, you're done!