Anger is one of the many emotions that we, humans, experience from time to time. It is a perfectly normal and healthy response to various situations that we are confronted with. The problem with anger is not that we feel it, it is that we aren't always the best at dealing with and expressing it appropriately. The Positive Discipline Tool: Anger Wheel of Choice can help.
The idea is to help your children learn that all feelings are okay, they just need to learn how to deal with them. During a peaceful moment, introduce the anger wheel of choice. You can use the free download here, or use it a an outline for you and your older child to come up with things that work for them. The next time that your child gets angry, invite him to use the wheel of choice to find an outlet that works for him.
We used an old spinner from a board game to make ours. Our, then 5 year old, daughter came up with her own tools for dealing with anger. They are: Read a book in bed, listen to music, draw or write about feelings, put it on the family meeting agenda, or have a hug. We also created a place in her room that she calls her peaceful corner. She has a giant teddy bear for sitting on and snuggling with, some beautiful pictures and a sound machine to listen to southing sounds. When she starts to get angry I can ask her if she would like to spin the anger wheel or take a Positive Time-out in her peaceful corner.
As with all the other tools, this only works some of the time. Sometimes it seems to make her more angry, but others it really, really, works, and when it does it is so great! Even if it only works one in ten times, I think it is worth it. Keep offering, if nothing else it is a way for you to consistently remind your child which responses to anger are appropriate and which aren't. This is a gift that can take them very far in life. Immagine if we all had the ability to deal with feelings in a peaceful and rational manner. It reminds me of something Montessori said, "Establishing lasting peace is the work of education; all politics can do is keep us out of war." That is to say, peace is an action we can teach/model, while war and conflict are emotional reactions. Let's teach peace!