How can one control ones emotions?

You can’t control emotions by thought; you can invoke emotions by thought. Only by being more aware, emotions settle down. Thoughts, emotions, and awareness; the more subtle and more basic level of consciousness. 

That happens and there is no 'how' to it; it just happens. Pranayama, meditation, listening to knowledge, all of this indirectly helps.

Usually the example would be, when you want to get the mango from the tree which is so high you hit the branch, you don’t hit the mango directly. Then you will not get the mango, you will only get juice on your head. You throw the stone in such a way the stone doesn’t land up on your head or on the mango but the mango lands in your hands. So you throw the stone at the branch and the mango falls. In the same way, all the techniques, everything we do is an indirect way to invoke consciousness. Got it?!