First of all, get protective gear to ensure that you are safe throughout. You also need a ladder to fix high walls. After this, you need to empty the room and open windows and doors to get fresh air.
The next thing is to place a drop cloth on the floor and start removing the old coat. After removing the old coat, you can go on to prepare the surface for a new coat.
The last thing is to prime the surface and apply new paint. You can also protect the newly-painted surface for some time if it is vulnerable to damage.