To remove your old internal door, start by propping the bottom of the door with a couple of wedges so it does not ‘drop’ as the hinges are removed.
Tip :- Screws that have been painted or varnished over will need to have the paint or varnish removed from the screw heads, this can be done using a small screwdriver, giving it a few light knocks will dislodge the paint or varnish, enabling the screwdriver tip to sit fully ‘home’ in the screw head slots. Use the correct size of screwdriver to suit the heads of the screws you are removing, aside making the job easier, this will help to prevent the screwdriver tip from slipping and rounding the screw head slot (s).
Remove all the screws from the door frame side of the bottom hinge first, have an assistant steady the door so it does not twist. Then remove all the screws from the door frame side of the top hinge.
The old door and wedges can now be carefully removed.
Unless the existing hinges on the old door are in very good condition and of an appropriate size, I would discard them and fit new hinges to the new door.
If you are looking for ideas for upcycling your old door, take a look at this board on Pinterest.
Now you are ready to start hanging the new internal door.