You put your belongings from the drawers into your suitcases, but you can leave things on hangers. On changeover day, your current steward, and your new steward will coordinate when to move things to the new room.
definitely do not put your suitcases out the night before the changeover.
they will give you a transit pass, which will allow you back onto the ship with minimal fuss.
they will also give you complete instructions in your state room, so read that paper carefully