I'll make this simple and I'll make this fast. (SOMEWHAT)
I wrote a long(liek 1000+ words) answer a while back about controling emotions, but I don't think the reader recieved it well because it didn't exsactly say how to do this, it merely stated the logic of the process, not the process. This time I'm going to break it down into something different.
There are several chemicals in the brain that make up our emotions.
There are chemicals that make you anticpate an action, enjoy the process of anction, and enjoy the completion of an action.
When emotions are 'pent up' its like to say there is an imbalance of the chemicals that make you anticpate something, making you restless and makeing the emotion stick. This is because you are unstatified... you have no completion and process to enjoy... just the anticaption... that will seemingly never end.
What you must do is accept for yourself a resolution. You must metally as and mean,' I will do this, and by doing it I will have my satifaction (or revenage or release, or, happiness, or peace or whatever it is that you need to remove this overwhelming burdon)'
This will create anticpation.
Then you do the action, and while doing it think... "This is helping me, this is working."
This will create a sense of success and pleasure during the action.
Then lastly, when you are done, say, "I'm done... and... now I'm at peace."
The action itself that helps you relieve stress shouldn't be something like lashing out, it should be something more peaceful, like drinking a whole glass of water, or writting a poem... or if you need to, crying, or a big shout.
These in of itself 'releases' the emotion that was 'stored' by making your brain balance your emotions. Sometimes its as easy as counting backwards from ten or saying your alaphabet backwards.
In the end, you should make yoursefl tranquil and calm. If you do something angry, and frustrated you could end up repeating the cycle, thus making yourself unstatified again.