I want to murder my brother
What did your brother do to you to make you want to murder him?
I don't like him anymore. He's an irritating person. Honestly, he treats me like I'm his slave sometimes.
Wanting to murder your brother shows that you really are upset with him. Maybe talking to him about why he has made you so upset would be the first option. If that doesnt work, then maybe try going to your parents or guardian to see what they think about the situation.
Ive decided, I'm going to murder him.
If this is a serious threat, then I will need to let someone know.  For you own safety, if you feel that something is unresolvable to the point, remove yourself from the situation distract yourself with something positive.