3D project to 2D

Hi all,
I created a mobile game with starter content but wish to turn it to a 2D sidescroller without any camera movement (puzzle game it will be).
Do I have to start a new project? If so, how do I import my level blueprint into it as the game logic is pretty much finished.
If this is unnecessary, right now I can fly around with wasd in the game, and it is basically a 3D project. How do I convert it to 2d?
Another EDIT:
I thought I clarify and write down one by one what I wish to change:
Right now I can fly around in the game after hitting the play button. I wish to turn that off, but I find no blueprint that would be responsible for the movement.
The game is 3D now. I want to have a 2D game, without camera movement.and without any lighting, post processing or any fancy rendering (to get it run the fastest possible). I have the pre-rendered images that will build up the level.
Also I need the camera to be orthographic instead of perspective. Please help me with those things as googling and try hasn’t got me far.