Close the door in the doorway. Insert the blade of a flat-head screwdriver under the head of the hinge pin on the bottom hinge and pry it up. Then pull the hinge pin out by hand or with pliers. Repeat this process for the other hinges on the door.
Pull the door out of the opening and set it aside. Unfasten the screws holding the hinges to the opening with a screw gun and set it aside.
Remove the trim around both sides of the door with a pry bar. If necessary, use a hammer to tap the pry bar between the walls and the trim. Set the trim aside once you have removed it.
Place a drop cloth in the opening and on both sides of the door to catch the dust and small particles as you cut out the doorway.
Put on safety glasses and a dust mask. Stretch a tape measure above the door and mark the two points where the new, expanded doorway or entryway will begin and end with a marker.
Use a chisel and hammer to hammer a hole above the doorway through each marked point on the wall.
Insert the blade of a reciprocating saw into the the starting hole and saw horizontally across to the other hole. Then saw from the top of the wall down to the floor. Break out the cut-out portion of the wall with a 5-lb. hand sledge to finish widening the doorway. You can now frame and finish the new opening.