Changing the CPU in a laptop is very difficult if not impossible for many reasons, including the way that laptops are built. They are not designed for easily changing the CPU, which may be soldered into place. Also, the BIOS may not support any CPU that is generally compatible with the CPU socket used, which again may not be of the type that allows you to change CPUs. The CPU cooling system may not be capable of supporting a higher TDP CPU as well.
You will need to check the construction of your laptops main board to see if it allows changing CPUs. Even if it does, doing so may void its warranty.
iv opened my laptop before and i can change the cpu i cant find the type of mother board anyware im trying to find the right cpu for my laptop
Try to get a cpu with the same pin configuration and number and if possible with the same model, which in your case would be a B940.
BTW a pair of pliers come in handy when unlocking the cpu.