Well, you might want to check what your horse is being fed with. Then, very hot horses needs to get out in the pasture\paddock as much as possible. He needs exercise, anytime you ride him have him free run in an indoor arena. Also watch out for the weather, cold excites them a lot, so you want to have him warmed up for about 15 good minutes before you ride him. If he doesnt respond to you when you ride him, use your legs well and any aid like pressure through your fingers. First start to have him calm in an indoor arena, then outdoor arena, then both of those with other horses with you doing random stuff near you, get him used to that, it takes time for horses and you need to be very patient. Once you feel him calm try to walk outside of the arena but around it if you can and enlarge the distance few by few. He just needs to be trained as many times as possible. If you do that everyday, in three weeks he will be pretty calm and spirited.