According to Tony Robbins, there is something called a Triad which is made up of 3 components which dictate emotional state. They are: physiology (physical), mental focus, & language (both self-talk & verbal).
When you find yourself in an emotional state or pattern that you would like to change you simply need to be aware of your Triad. By taking out one of the pillars, you disable the ability for that emotion to have control over you. Practicing this alteration allows you to build up your emotional "muscles" thereby strengthening you emotionally.
Think of how you hold yourself when you are sad or depressed. Your head is down, your shoulders are slouched, and you speak in a soft tone.
You can not feel that emotion if you pick up your head, bring your shoulders back, and speak in a firm voice. If you believe that you can it is only because you are consciously trying to prove the theory wrong and forcing the emotion to stay in an unnatural state.
Identify which emotions you are trying to break away from & how you carry yourself, how you speak, what your inner dialog is like, and what your mind is focused on ~ then change it!
Hold your body in the position of the emotion you want to be feeling instead. Tell yourself things that you would say if you were already in that emotional state and with the same tone you would be using if you were there. Focus your mind on where you want it to be.
Practice makes perfect - so repeat this over and over as much as possible until it becomes natural & you are able to shift your emotional state at will.