What is the best way of changing player models?

So some games have vehicles in which you can sit in and your character is basically controlling the vehicle, weather is be a mech,car,helicopter or a jet. Now I know that you can make startercharacter as this model for player to spawn as but I need it to be like when you sit on a seat all your camera,humanoid and all gets transferred to the model where you can use your WASD keys to move