Car Alarm

The alaram goes off if I don’t start the car right away. The car makes the door locking sound and I have seconds to start the car or the alarm goes off. Also, the doors do not always lock on the first try. I have to unlock and relock. Realted problems? Can I disconnect the alarm without affecting the horn? How do I disconnect the alarm? I have a shop manual. My car is green (is that the problem?) with 112,000 miles. I love my car.