Adjust the speed limit value at the current speed: press the key 2 or 3 short, and set the speed value to increase or decrease by 1km/h; Press and hold the key 2 or 3 for a long time and set the vehicle speed to 5 km/h.

How to adjust the car speed limit to 40 km/h depends on whether the car you are driving has this function. Some vehicles may have an adjustable cruise control system that allows you to control the speed while driving. If your vehicle is equipped with adjustable cruise control, you can adjust the speed to 40 km/h through the button on the controller. However, the speed limit of most cars is controlled according to road signs and speed limit systems, not by individuals manually.

Therefore, if you want to know how to adjust the speed limit of a car to 40 km/h, please consult your vehicle manual or contact your car manufacturer or dealer for more information. At the same time, please pay attention to strictly abide by local traffic rules and road speed limit signs.