Is it possible to change the freon in one's car ac by oneself? Is it complicated?

all depends if the car takes R-12 or R-134a. if it takes R12, then you cant do it yourself, it is illegal for a shop to sell R-12 to anyone without a EPA license. if it is R-134a you can buy the self recharge cans and fill it up yourself. however you have to take special care to not overfill the system as that can cause severe damage to the system.