The answer to how to stop being angry would be just to tell yourself not to get angry. It is as simple as that. Sometimes, all you need are a few words of self-encouragement to get yourself going. In your head, tell yourself that if you are faced with a particular challenge, react with a different emotion other than anger.
Write down a few test scenarios and practice it out with friends. Next to each bad scenario, write two different reactions – the angry one and the calm one. List the benefits of remaining calm and then list the disadvantages of getting angry.
For instance, enact a common scene in a restaurant. Have a friend “accidentally” spill food on your new suit and decide how you plan to react to this bad situation. A typically angry person will react very poorly and “flip his top,” as they would say. He may rip off the suit, cause a scene and get thrown out of the restaurant. A less angry person will wipe off the mess, make amends with the friend and remain calm throughout the situation. In hindsight, which scenario is more preferable is mostly a no-brainer.